TUESDAY, SEPTEMBER 15.

The following Papers were read :—

1. Note on Pearl-formation in the Ceylon Pearl Oyster.

By Professor W. A. HERDMAN, D.Sc., F.R.S., and JAMES HORNELL. Professor Herdman and Mr. Hornell have had two cruises of several weeks each amongst the pearl-oyster banks in the Gulf of Manaar, and have had the experience of the three consecutive inspections of March and November 1902 and March 1903, and also the successful fishery of 1903, from which to draw conclusions. Many hundreds of oysters have been examined, and large numbers of pearls have been decalcified. As a result of this work they have come to the conclusion that there are several distinct causes that lead to the production of pearls in the Ceylon pearl oyster' (Margaritifera vulgaris, Schum.).

1. Some pearls or pearly excrescences on the interior of the shell are due to the irritation caused by Clione, Leucodore, and other boring animals.

2. Minute grains of sand and other inorganic particles only form the nuclei of pearls under exceptional circumstances. Probably it is only when the shell is injured, e.g. by the breaking of the ears,' thus enabling sand to get into the interior, that such particles supply the irritation that gives rise to pearlformation.

3. Many pearls are found in the muscles, especially at the levator and pallial insertions, and these are formed around minute calcareous concretions, the 'calcospherules,' which are produced in the tissues and form centres of irritation.

4. Most of the fine pearls found free in the body of the Ceylon oyster contain the remains of Platyhelminthian parasites, so that the stimulation which leads to the formation of an 'Orient' pearl is, as has been suggested by various writers in the past, due to the presence of a minute parasitic worm. In all cases, whatever its nucleus may be, the pearl, like the nacre, is deposited by an epithelial layer.

These pearls may be conveniently classified as

T. Ampullar pearls, where the nucleus and resulting pearl lie in a pouch, or ampulla, of the ectoderm projecting into the mantle. The others lie in closed sacs. II. Muscle-pearls, formed around calcospherules near the insertions of muscles. III. Cyst-pearls, formed around encysted parasites. The parasite in the case of the majority of the cyst-pearls of Ceylon is the larva of a Cestode which appears to be new, and will be described under the name Tetrarhynchus unionifactor. The younger larval stages have been found free-swimming in the Gulf of Manaar and on the gills of the oyster; later stages are common in the liver, mantle, and gills; and a more advanced Tetrarhynchus is found in the file fishes, Balistes mitis and B. stellatus, which feed upon the oysters. The sexually mature Cestode has not yet been found, but we may expect it to occur either in one of the large Elasmobranchs (such as Trygon uarnak) which abound on the pearl banks, or possibly in one of the smaller cetaceans, which may also feed upon such fishes as Balistes.

2. On a Phosphorescence Phenomenon in the Indian Ocean.
By Professor W. A. HERDMAN, D.Sc., F.R.S.

Professor Herdman described how during his recent expedition to Ceylon, as they lay at anchor in the Gulf of Manaar, on March 13, 1902, about 9 P.M., the sea was seen to be dotted with bright phosphorescent lights, of considerable size, singly placed at some distance apart. These for over an hour continued to glow with a pulsating appearance in harmony, all shining brightly at the same moment, and then all flickering out together, to reappear simultaneously a few

seconds later. On going out at once with a net a sample of the plankton was obtained, but it was not certain that any of the pulsating forms had been caught. The gathering contained Sagitta (very many), Appendicularia, Copepoda, several common species and Sapphirina sinuicauda, Pontella fera, Calocalanus pavo, and some smaller forms, along with half-a-dozen one-inch-long Heteronereids of a reddish-brown colour. The light was thought to be probably due to the last named, and if that is so possibly the periodicity was a result of the epitocous condition, and was accompanied by a simultaneous discharge of genital products. The matter, however, could not be made certain at the time, and the above explanation is only suggested.

3. Note on Birds now rare in the British Isles.
By G. P. HUGHES, F.R.G.S.

The author gave a brief account of a male and female Bittern shot at the base of Cader Idris last winter, and of a Common Crane he lately saw in the valley of St. John, Isle of Man, species now rare in the British Isles.

4. Demonstration of Visual Combination of Complementary Colours. By C. A. GREAVES, M.B., LL.B.

The author showed that the difficulty in visually combining different colour sensations so as to perceive the resultant is overcome in the case of green + red = grey by the use of the present halfpenny and penny stamps, stereoscopically superposed, these stamps being identical in design and of gocd complementary colours.

5. The Epithelial Islets of the Pancreas in Teleostei.
By JOHN RENNIE, D.Sc.

It has been found that in all the leading divisions of this group there exist in more or less intimate relation to the pancreas epithelial bodies similar to the 'islets' present in higher forms. In a large proportion of cases there is an islet in the mesenteric fold anterior to the spleen, which is of constant occurrence. It is also the largest. As similar constancy has not been made out for the others it has been termed the 'principal islet.' These bodies are an epithelial tissue consisting of masses of very small polyhedral or cylindrical cells well supplied with blood capillaries. In many cases two types of cell are evident within the islet. which may be two distinct tissues or the same tissue in different functional states. A comparative study of their relations to the zymogenous tissue of the pancreas suggests that they are blood glands which have entered into a secondary relation to the pancreas. It is likely that they maintain their primitive function as glands possessing an internal secretion.

6. On the Echinodermata of the Firth of Clyde and Variation in Ophiocoma nigra.1 By D. C. MCINTOSH, M.A.

In this paper, which dealt with the Echinodermata of the Clyde area, notes were given on the frequency of the occurrence of the different genera and on some of the most obvious variations exhibited by certain of the species. The daily dredging expeditions of the steam yacht 'Mermaid,' which is run in connection with the West of Scotland Marine Biological Association Station at Millport, afforded one ample opportunity for making the necessary observations.

It was pointed out that while forty-two species are recorded for the Clyde (against at least thirty-five for the Irish Sea), there were actually found during

Published in Biometrika, vol. iv.

the autumn of 1902 thirty-three species, viz. Holothuroidea 8, Crinoidea 1, Asteroidea 11, Ophiuroidea 7, and Echinoidea 6, the most common genus of each of these orders being Synapta, Antedon, Asterias, Ophiocoma, and Echinus. Note was taken of the very considerable variations in the shape of the test of Echinus esculentus and in the number of arms of certain of the Asteroidea.

The remaining part of the paper was taken up with a discussion on the variation of Ophiocoma nigra (O. F. Müller), and an account was given of the results obtained from an examination of certain external features of 3,000 specimens of this Brittle-star. An attempt was made by means of diagrams to classify the shape and colour variations of the disc. It was found that the disc tends to become circular in the more fully developed animals, but that it is in general pentagonal and not round. Twenty-four per cent. showed no colour variation, while 64 per cent. had a pentagonal yellowish central disc marking. In 12 per cent. of cases this marking was small and circular. The correlation between arm-length and disc-breadth was worked out by the methods followed in 'Biometrika,' and a table was given showing the number of animals having a certain disc-breadth associated with a certain arm-length. The equation to the 'Line of Regression' of arm-length on disc-breadth was

y = 4·89623x + 1·17469962,

and this was shown by means of a diagram to represent very closely the observed facts. The mean disc-breadth and arm-length were respectively 10 106 mm. and 50-656 mm., a relationship which is very noteworthy in view of the important part which the number five plays in the arrangement of the organs of the Echinodermata. A Polygon of Frequency' based on the disc-breadth was given, and also the curve whose equation is

y =

185-57 (1-5-3264)

which best fits it. Tables were added showing that 13 per cent. had more than one madreporic plate, and that out of 3,000 specimens thirteen had an abnormal number of rays, there being one Brittle-star with only four arms and twelve with six arms each.

7. Note on the Eggs of the Shanny (Blennius pholis, L.).
By Professor W. C. MCINTOSH, M.D., F.R.S.

In the life-histories of the British food-fishes, published by Dr. Masterman and the author in 1897, it is stated that the eggs of this fish had not hitherto received satisfactory attention. In June of this year an adult female, 43 inches in length, was captured with enlarged ovaries. On the morning of June 5 it was found to have discharged a number of golden eggs, each having a faintly' pinkish disc for fixing it to stones and other surfaces. As attached to glass, each egg was circular in outline with a distinct hyaline zona, the contents being dull pinkish or pale salmon. This tint was enlivened by a series of bright yellow granules and masses (oil-globules). The egg formed an oblate spheroid, the vertical diameter being 7630 mm., whilst the transverse diameter ranged from 1·1811 mm. to 1·2192 mm. The breadth of the pale pinkish rim for attachment was about 3048 mm. Many of the discs had a finished appearance, whilst in others the edge was spongy, with projecting processes. In minute structure the whole is granular. Allusion is made to the observations of Dr. Scharff on the structure of the peculiarly modified ovarian follicle of the shanny and the remarkable hardihood of the fish, which can be kept for a week at least in fresh water. The proportion of males and females is also mentioned. The food of the shanny at St. Andrews largely consists of the stunted small and young mussels, Balani, small univalves, such as young Littorina and adult Rissoæ, with fragments of limpet.

DEPARTMENT OF PHYSIOLOGY.

1. A Physiological Theory to Explain the Winter-whitening of Birds and Mammals in Snowy Countries, and the most Striking Points in the Distribution of White in Vertebrates generally. By Captain G. E. H. BARRETT-HAMILTON.1

The subject of the winter-whitening of animals, though of much interest to zoologists, is very imperfectly understood. Most writers are satisfied to believe that the colour change originated somehow under the action of natural selection for the protective purposes of adaptation to environment.

The author finds, however, that the change has a deep physiological significance. There is, for instance, in mammals a definite sequence in which the various parts of the body whiten. This sequence, on the whole, corresponds to the summer accumulation of fat in the panniculus adiposus. Thus the belly, where peripheral fat is thickest, is permanently white, and the rump, often the next thickest area of fat accumulation, is usually the first part to whiten in winter.

Many northern mammals and birds not usually regarded as of this category are lighter in winter than in summer. The white assumed in the former season corresponds to the fat-tracts, and they may be therefore regarded as subject to the same process.

In the northern summer most animals accumulate fat, always in a definite manner as regards the regions where it is deposited. This fat is indicative of deficient oxidisation and sluggish metabolism, and the process of its accumulation is therefore one of atrophy. The fat-accumulation and atrophy is most marked in autumn, at which season metabolism is lowest. Under the onset of winter cold the atrophy may extend to the hairs. Their pigment (as observed by Metchnikoff) is then removed, always, however, first in those parts where peripheral fat is thickest, and atrophy therefore greatest. Should there be a change of coat at this time the new hairs are influenced by the same conditions. In very cold countries they come up white all over the animal; in more temperate regions the parts only where fat is thickest are white.

Although a pigmented hair can thus undergo atrophy and loss of pigment, the author knows of no case where the colour is replaced. Animals once whitened remain so until the spring moult.

These facts apply broadly to birds and mammals, but the variable hare and stoat are those which have been studied especially.

The same law is responsible for much of the distribution of the white colour throughout the vertebrate phylum, wherein the connection between the white colour and the peripheral fat-tracts (thus indicating local atrophy) may be widely traced. Thus domestic animals, nearly all of which are prized most for their power of accumulating fat, exhibit a strong tendency to the development of white patches. In both these and in wild animals the belly, where occurs the principal fat-tract, is the most frequently white part; next follow the rump, neck, and parts of the limbs and of the head.

Marked exceptions are no doubt frequently due to unusual arrangements of the panniculus adiposus. Thus in the badger, a representative of a family in which the back is usually whiter than the belly, a correspondingly exceptional arrangement

of the fat-tracts occurs.

The white of the head-the 'blaze' of horses and the facial stripes of the badger, for instance-affects regions, not of fat-accumulation, but where the skin immediately overlies bone and membrane (frontals, nasals, and zygomatic arches), which thus seem to produce an atrophy similar to that caused by underlying fat.

In many animals the hair-atrophy assumes the form, not of whitening, but of baldness. Marine mammals are hairless in proportion to their fatness; fattening cattle lose their hair, while the baldness of man corresponds in position to the 'blaze' of horses, and the bare buttocks of monkeys to the white rumps of other mammals.

Will appear in the Proceedings of the Royal Irish Academy.

Yellow and red frequently follow the same rules of distribution as white. They are well known to be fat-pigments.

The author carefully guards himself against the extension of his theory to all cases where white occurs in vertebrates. It is obvious that not ali animals are subject to this atrophy, and there must be other causes for absence of pigment. It seems highly probable from what the author has written that the known unevenness of animal coloration is but the external indication of uneven nutrition in different regions of the body.

2. A New Form of Osmometer for Direct Determinations of Osmotic Pressure of Colloids. By Professor BENJAMIN MOORE, M.A., D.Sc.

This form of osmometer has been specially designed to avoid leakage and provide a large surface for diffusion compared to the volume of solution employed, so that the influence of crystalloids is made slight and transient. To effect the first purpose the instrument is made in metal in two halves which can be tightly screwed together by a collar, and the two halves are further made up of two shallow cells, to hold the solution and solute, so that the influence of admixed crystalloids is rapidly eliminated by diffusion.

The instrument essentially consists of two flattened circular cells of platinum 1 5 cm. in diameter and 1 cm. in depth, with flat flanges at their rims which fit into corresponding thick flanged cases of silver-plated brass. The brass cases can be screwed tightly together by a brass collar with a female screw at one edge, which engages with a male screw on one of the brass cases, and a flange on the other edge which catches on the flange of the other brass case.

1

A diaphragm of platinum bored closely with holes about 3 mm. in diameter is placed between the two cells, and serves to support the membrane of parchment paper which separates them.

The instrument is made pressure-tight by two rings of thin indiarubber sheeting placed on either side of the diaphragm, and when the collar is securely screwed home has in all cases been found free from any trace of leakage.

A platinum tube of about 4 mm. diameter leads, at right angles, from the centre of the back of each cell, and is used to connect up for filling and registering the pressure.

The large surface provided for diffusion compared with the volume of solution assures an early equilibrium of crystalloids. When a 1 per cent. solution of sodium chloride is placed on one side and distilled water on the other, there is no appreciable movement in the attached mercurial monometer, and within twentyfour hours the amount of sodium chloride on the two sides is equal within the limits of experimental error.

The connecting tube on the side of the colloidal solution is joined up by rubber tubing to a T-piece, which is in communication by one arm with a glass funnel and by the other with a mercurial monometer. On the side of the solute (water) the cell is simply joined by rubber tubing to a funnel.

In using the apparatus the connections are first filled with the respective fluids and temporarily clipped off, then the cells are filled in turn and joined up, all air being expelled by pressure upon the rubber connections.

The two funnels upon either side are fixed at an equal height, of about 20 centimetres in each case, above the instrument, so as to ensure initial equality of pressure on the two sides of the membrane.

The osmometer is then suspended in a large vessel of water for the purpose of maintaining a constant temperature, which can be arranged at different levels by a thermo-regulator.

When the desired temperature has been attained, the osmometer is clipped off from the funnel connection on the solution side and left in communication with

1 In earlier experiments the platinum lining was dispensed with and the silverplated brass case only used. This makes the instrument much less expensive, and is effectual unless when the action of reagents, such as alkalies and acids, upon the colloid is to be tested.