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common shrimp from Plymouth to be only 0:11. Perhaps this difference may in part be accounted for by the fact that the prawn is essentially a swimmer, while the shrimp, in confinement at any rate, spends most of its time standing or crawling on the surface of the sea-bottom. The prawn is certainly a more powerful and rapid swimmer. It swims backwards, propelling itself by means of the hinder part of the abdomen, the terminal portion of which is fanshaped, the fan consisting of the telson and the exopodites of the last pair of appendages. This hinder half of the abdomen starts from the extended position, and is brought, with a rapid stroke, up under the fore part of the abdomen and thorax, pushing the water before it, and so propelling the animal backwards. The 3rd seg. ment acts as the hinge of the propeller, and it may be assumed that the exoskeleton is here exposed to the greatest strain, for here we find the highest degree of correlation, as is shown by the following figures :

Index of correlation between terga of abdominal segments 1 and 2 0:58.

2 3 = 0.70.
3 4 = 0-71.

5 0.62,
5 6 0:57.
6 and
telson = 0:51.

Professor Weldon determined three other values in the shrimp, viz., the relations between carapace length and post-spinous portion of carapace, between carapace length and tergum of abdomen vi., and between carapace length and telson. Their values were (in Plymouth specimens) 0.81, 0·09, and 0·18 respectively. It is not possible to institute a comparison with exactly the same organs in the prawn, as, owing to the great variation in the length of the rostrum, no appreciable degree of correlation exists between the whole carapace including rostrum (measurement No. III) and the other organs. Bui if we take measurement No. II (from orbit to, hinder edge of carapace) as an approximate equivalent to the carapace measurements of the shrimp, we find in the prawn the corresponding values are 0·59, 0·59, and 0.40. The difference in the first measurement, viz., shrimp, 0-81; prawn, 0:59, may be accounted for by the fact that the dorsal spines probably do not correspond in nature or function in the two animals. The shrimp has but one median dorsal spine, situated far forward; the prawn has a row of them.

But why the prawn should exhibit a so much higher degree of correlation between the carapace and the two terminal segments of its body than the shrimp is not, I think, readily to be ex

plained at first sight, unless it be due to difference in habits of locomotion above referred to.

The subjoined table furnishes the necessary data for constructing approximately the curve of each of the separate organs.

The Roman numerals in the first column refer to the organ described above under the corresponding numbers on p. 235; the second column contains the number of animals ont of the whole sample of 1000 in which a measurement of the particular organ was made; the third column contains the median value; and the fourth the "probable error” or quartile deviation from the median of each organ expressed in thousandths of the body length; the fifth and sixth columns refer to the same animals after subtracting from their number thirteen individuals in which the rostrum or telson was deformed, and for these the arithmetical mean and probable error (obtained by finding the mean error and multiplying it by 0.845) are given.

All the figures in columns 3 to 6, inclusive, represent thousandths of the body length, except those standing against organ No. I (the body length itself), which represent millimetres.

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I
II

VI
VII
VIII
IXa
IX.
X
XI
XII
XIII
XIV

XV
XVI
XVII
XVIIIa
XVII16
XIXα
XIX.

1000 1000 1000 1000 998 998 998 997 976 967 863 999 1000 1000 999 997 992 998 971 719 571 572

88.03 200.40 462.20 130.31 306.88 179.39

42.94 155.01 159.70 160.98 83.98 42 •37 101:49 134.72 114:14

77 .32 112.39 134.82 120.84 120 •73 33 33 33.25

4.85 3.46 7.19 9.83 8.18 8.16 2.39 3.66 3.29 3.26 1.79 1:19 2.08 2.52 2.37 1.61 2:19 2.65 2.25 2.36 2.55 2.46

88.20 200.43 462.56 129.84 306.95 180.39

43:11 155 02 160.04 160.58 83.91 42.21 101.40 154 69 113.97

77 .22 112.30 134.83 120.88 120.70 33:33 3:3 .27

4.91 3.49 7.26 10:46 8:12 9.02 2:34 3.78 3.28 3.24 1:77 1:17 2.12 2:55 2.33 1.63 2.26 2 61 2.21 2:31 2.73 2.59

VOL. LY.

S

In conclusion, I desire to express my warm thanks to Professor Weldon for constant advice and assistance on many points connected with the preparation of the foregoing data.

Presents, March 1, 1894. Transactions. Baltimore :-Johns Hopkins University. Circulars. Vol. XIII. No. 109. 4to. Baltimore 1894.

The University. Béziers :-Société d'Étude des Sciences Naturelles. Bulletin. Vol. XV. 8vo. Béziers 1893.

The Society. Bordeaux :-Société de Médecine et de Chirurgie. Mémoires et Bulletins. 1892. Fasc. 3—4. 8vo. Bordeaux 1893.

The Society. Cracow :--Académie des Sciences. Bulletin Internati al. Janvier, 1894. 8vo. Cracovie.

The Academy. Freiburg i. B.:-Naturforschende Gesellschaft. Berichte. Bd. VIII. 8vo. Freiburg i. B. 1894.

The Society. Genoa :-Società Ligustica di Scienze Naturali e Geografiche. Atti. Vol. IV. Nos. 243. 8vo. Genova 1893.

The Society. Kingston :-Institute of Jamaica. Journal, Vol. I. No. 8. 8vo. Kingston 1893.

The Institute, London :- British Museum. Catalogue of the Birds. Vol. XXII, 8vo. London 1893.

The Trustees. Institute of Brewing. Transactions. Vol. VII. Nos. 3–4. 8vo. London 1894.

The Institute. Royal Horticultural Society. Journal. Vol. XVI. Parts 2—3. 8vo. London 1894.

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No. 89. 8vo. London 1894; The Meteorological Record.
Vol. XIII. No. 50. 8vo. London.

The Society. Royal United Service Institution. Journal. Vol. XXXVIII. No. 192. 8vo. London 1894.

The Institution. Lyons.-Université. Annales.

Annales. Tome VI. Fasc. 3. : 8vo. Lyon 1893.

The University. Marseilles :-Faculté des Sciences. Annales. Tome III. Fasc. 143. 4to. Marseille 1893.

The Faculty. Melbourne :-Royal Society of Victoria. Proceedings. Vol. VI. . 8vo. Melbourne 1894.

The Society. Mexico :-Sociedad Científica “Antonio Alzate." Memorias y Revista. Tomo VII. Nos. 5–6. 8vo. México 1893.

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Section des Sciences. 2e Série. Tome I. Nos. 1-2. 8vo.

2

Transactions continued).

Montpellier 1893; Section de Médecine. 2e Série. Tome [.
No. 1. 8vo. Montpellier 1893; Section des Lettres.
Série. Tome 1. Nos. 1–3. 8vo. Montpellier 1893.

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The Museum. Palermo :-Circolo Matematico. Rendiconti. Tomo VII. Fasc. 6. 8vo. Palermo 1893.

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Tome XXI. Nos. 1-3. 8vo. Paris 1893. The Society. Rome :-R. Accademia dei Lincei. Annuario 1894. 8vo. Roma 1894.

The Academy Siena :-R. Accademia dei Fisiocritici. Atti. Vol. V. Fasc. 910. 8vo. Siena 1894.

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The Academy. Topeka :- Kansas Academy of Sciences. Transactions. Vol. XIII. 8vo. Topeka 1893.

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The Academy Vienna :-Anthropologische Gesellschaft. Mittheilungen. Bd. XXIII. Heft 6. 4to. Wien 1893.

The Society. Washington :-U.S. Department of Agriculture. Experiment Station Bulletin. No. 18. 8vo. Washington 1894.

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Observations and Reports.
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No. 4. 8vo. Albany 1894.

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The Observatory.
India :-Census of India, 1891. General Report, by J. A. Baines.

Folio. London 1893; General Tables for British Provinces
and Feudatory States. Vols. 1-II. Folio. London 1892–93.

The India Office.
London :-Admiralty. List of Oceanic Depths and Serial Tempera-

ture Observations received at the Admiralty during the year
1893. Folio. London 1894.

The Hydrographer.
Marseilles :-Commission de Météorologie du Département des

Bouches-du-Rhône. Bulletin Annuel. Année 1892. 4to.
Marseille 1893.

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Paris :-Bureau Central Météorologique. Annales. Année 1891.

4to. Paris 1893 ; Rapport de la Conférence Météorologique
Internationale: Réunion de Munich, 1891. 8vo. Paris 1893.

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Observatoire. Annales : Observations. 1885. 4to. Paris 1893.

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teorological, Magnetical, and Solar Observations. 1893. 8vo.
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