terminates abruptly with the 17th vertebra, and no caudal chain of interspinous bones can be traced. The liver is small, when compared with that of the young Orthagoriscus, and is composed principally of a large right lobe overlying the stomach. The stomach is small and the intestine is short, making but two turns, like the letter S, while in Orthagoriscus it is long and has five or six turns, or coils. The arrangement of the muscles and the bones of the head are, in general, about the same as in Orthagoriscus.

Figure 134 is from a specimen of Molacanthus Palassii,* natural size. This specimen was taken from the stomach of a dolphin caught in the North Atlantic and belongs to the Boston Society of Natural History.

Figure 135 is the young of Orthagoriscus (Cephalus) oblongus, copied from Harting's Memoir. This specimen was taken from the stomach of a "Thon" caught in the Atlantic Ocean, and is represented of natural size. Figure 136 is from one of the young specimens of Orthagoriscus mola taken in Massachusetts Bay. Natural size.

Figure 137 represents the adult form of Orthagoriscus mola from a drawing of a specimen taken in Massachusetts Bay in 1856. Length forty-two inches; width from tip of dorsal to tip of anal sixty-four inches. This specimen was fully developed and shows the characteristic "nose" of the older individuals, the backward position of the eye and the position of the fins. None of the published figures of the adult are very correct in their outline. The best is that of Harting, under the name of Orthagoriscus ozodura, in the Transactions of the Academy of Amsterdam for 1868. An intermediate stage between the young and the adult, here figured, is represented by the figures of Bloch, Donovan, and Yarrell.

Dr. R. H. WARD read a paper before the Section of Microscopy "On the Illumination of Binocular Microscopes." The object of this paper is not to add anything to the facilities at the command of specialists in microscopy, whose devotion to narrow branches of study, often accompanied by ample means to command every assistance within the skill of the opticians, has brought into existence the sumptuous first-class stands and their elaborate accessories, but to make some suggestions in the interest of that larger class, microscopical amateurs, who, incidentally to other occupations, use the instrument for the general study of natural history. Such persons usually, and wisely, buy the smaller instruments of the market, and their choice of apparatus, and consequent success in work, depends much upon the chances of trade and the interested partiality of dealers.

It is not strange, but unfortunate, that this class of apparatus, students'

*The synonymy of these fish will be discussed in full in the Memoirs of the Academy. The names now used are those under which the species are most generally known..

Mr. Putnam's paper will be published in full in a future number of the Memoirs of the Peabody Academy of Science, with several plates, illustrating more fully the points mentioned in this abstract.

microscopes, et id omne genus, should latest and least feel the control of real science in their construction. Only a few years ago in London, and much later in this country, was there any serious effort to make students' microscopes worthy of the times. Even now some of the best of these are sold without a diaphragm below the stage, or with so small a body that the lowest (and, for beginners, best) eye-piece gives a ridiculously small field, and too many are still built upon the old vertical plan which has been obsolete for twenty years. In regard to stereoscopic microscopes the case is still worse. Tolles' binocular eye-piece "for microscopes only" is not yet in the market, though expected for years, and Wenham's binocular, long since popularized in England, is nearly unknown here except on large and costly instruments. Grunow, of New York, has done something during past years to furnish small binocular instruments. When will he, and Tolles, and Zentmayer, and Miller, and McAllister, and others, do for us what Crouch, and Collins, and Murray and Heath, and Beck, and many others, have long since done for England in supplying an abundant variety of good binoculars of moderate size and cost? If the binocular microscope were unnecessary for anybody it would be for the diatomist; yet I can scarcely believe that such a person, after seeing a Möller's type plate properly illuminated under a 4-10 objective of 110° or 120° in a good binocular, would ever advise any person to purchase a monocular instrument except as a necessity of price. While we are waiting for still further improvements in the binocular, promise of which may be seen in Mr. Holmes' bisected lens, the erecting binocular of Mr. Stephenson, and the binocular by double refraction of Dr. Barnard, let the contrivances already available, Wenham's for low and medium powers, and Tolles' for high powers, be made to do all the good they can do. We should take care that in simplifying our apparatus we do not gain simplicity at the expense of convenience. Of the three elements in microscopical work, the object, the amplifiers, and the light, the latter is the most difficult to handle and is least satisfactorily provided for. If any one accustomed to use a microscope which has no control of its light except by a mirror and diaphragm, will temporarily replace the diaphragm by a sliding tube capable of holding his highest power eye-piece and of focusing it from below upon the object, he will be little likely to use the instrument afterward in any other way. A Kelner's eye-piece. suggested as a condenser by Mr. Brooke, and urged by Dr. Beale, would be still better; and probably Tolles' orthoscopic eye-piece would answer the same purpose. The illuminating angle would be varied by focussing below the object, with much less loss of definition than in the old style of using an objective for the same purpose; or, preferably, various stops of blackened card would be introduced below the field-lens to stop off any desired portion of the light, and similarly a disc of blue glass would be used to correct the yellow glare of artificial light. With slight mechanical ingenuity the student can combine these stops in a circular diaphragm of blackened card or brass, and somewhat increase the convenience of

his really excellent achromatic condenser. The efficiency of his apparatus will be vastly increased by adding the graduating diaphragm made by Collins and others in London and occasionally offered for sale in this country. Or, at a very reasonable expense, he can order the Webster condenser and graduating diaphragm complete of Collins or Crouch, or other London dealers. At first sight it would seem that this apparatus could not be used on stands of the Jackson" model; but, by a little judicious filing, it can be used on large stands of this style, as I have been accustomed to do for years. After using a graduating diaphragm in the ordinary microscopical work of natural history, the orthodox wheel of apertures, with its intermittent views of the object, and its abrupt changes of light, seems simply absurd. For use without a condenser, or with one of the large lens or eye-piece form, Collins' graduating diaphragm should be used on all stands to which it can be applied; otherwise, and especially with the small lens or objective form of achromatic condenser, Zentmayer's graduating diaphragm should be used, or Brown's iris diaphragm as made by Beck. There is often some difficulty in getting the graduating diaphragm sufficiently near to the lenses in the small lens condensers, but none in the eye-piece condensers.

The easiest and most fascinating use of the stereoscopic microscope is doubtless with opaque or translucent objects with the paraboloid or other means of black-ground illumination. In lighting transparent objects under the binocular we have only one new condition introduced, the necessity of a wide horizontal illumination in order to give an even light over the whole of both fields. Focussing the condenser upon the object and gradually opening the diaphragm, we shall probably find, with a 1inch of 25°, the best definition and resolution accomplished just at the point where both fields are fairly lighted; but with a 1-2 of 60° or a 1-4 of 75° the best definition is often gained when each field is scarcely halfilluminated, and when the fields are wholly lighted the object is nearly drowned. If we now open wide the diaphragm, and introduce a blackened card disc punched with two holes (Plate 5, fig. 5) so as to give two cones of light each having an angular width about one-half or one-third of that of the objective, and converging horizontally upon the object at an angle nearly as great as that of the objective, we shall have both fields fairly and evenly lighted, and no glare. The same end is attained by a stop with a horizontal slit, giving a wide horizontal and narrow vertical pencil of light.

This expedient may be applied with some advantage even to instruments without accessories, by placing a disc like Fig. 1 of Plate 5, having an opening of suitable width, over the diaphragm, to shape the cone of light from the concave mirror; or the regular wheel of apertures may be replaced by a somewhat larger one containing one or two openings of this shape.

Next comes the spotted lens, which may be applied to any microscope and which will greatly increase its working power at an almost nominal

expense, giving sufficiently good black-ground and oblique-light effects for small microscopes. This lens is used for transparent illumination of both fields of the binocular with 1-2 or 1-4-inch objectives (the Webster condenser, with its smallest centre stop, and graduating diaphragın, attains the same end in a much finer manner), but much of the light passed even by it is detrimental, and its performance may be improved by a cap of card or paper, placed over it, having a horizontal opening, or a vertical stop (Plate 5, figs. 2 and 3), one of the openings in Fig. 3 being closed when oblique light is required. A horizontal opening of adjustable width may be easily combined with the brass mounting of the spotted lens.

In using an objective or similar combination as achromatic condenser the horizontal slit is still more applicable. It (Plate 5, fig. 4) may be added, for instance, to the stop-plate of Powell and Leland's achromatic condenser, or placed in the supplementary aperture of Ross' 4-10 condenser, or in small microscopes screwed in between the lenses of a condensing objective. Different stops must be used for different angles of width required, 25° or 30° being generally applicable and the length being regulated by the diaphragm-plate, or by Zentmayer's graduating diaphragm, or Brown's iris diaphragm which, instead of the diaphragmplate, should be combined with condensers of this class.

But the real value of this stop, and the real ease of handling the light in the every-day work of the stereoscopic-microscope, is attained with the large-lens condensers, with which a 1-4 of 75°, or, when more resolving power and less depth of field is required, a 4-10 of 110° to 120°, can be as easily managed as a 1-inch, both fields being softly and evenly lighted. Paper discs like Plate 5, fig. 5, may be used, adapted to various powers and placed between the lower lens of the condenser and its stop-plate, or Plate 5, fig. 6, may be placed in the same position, or the stop-plate may be so modified as to furnish a horizontal slit as in Plate 5, fig. 7, the length of the slit being controlled by the graduating diaphragm. An adjustable slit may be extemporized by using a straight edge of card in connection with the oblique stop of the stop-plate; or it may be combined with the brass-work as a pair of shutters somewhat like those of the spectroscope, or as a supplementary wheel, like Plate 5, fig. 8, above the usual stop-plate. The large round opening in this plate (Fig. 8) should be furnished with a rim to carry any experimental stops of blackened paper that may be desired. If the two plates are of exactly the same size and properly mounted at the centre, there is not the slightest difficulty in moving each independently of the other; nor is the unequal width and curved direction of the slit any serious inconvenience in practice.

The graduating diaphragm, for facility of use and certainty of results, has fairly superseded the original wheel of apertures; perhaps the time may come when we shall equally discard the wheel of stops, and have nothing left to remind us of our circular diaphragm-plate. If the opticians would give us something having the general arrangement of the