54 REPORT — 1855. 



In Caprella Pennaniii two distinct circular orifices, situated side by side, as 

 in the highest types, are visible in the calcareous ventral aspect of the fifth seg- 

 ment. This is also confirmed by Rousel de Vauzeme in his observations on 

 Ci/amus ovalis, except the organs which he appears to raise on small pro- 

 minences (PI. XIII. fig. ITa.a, Ann.des Sc. Nat. 1834-). The position of these 

 organs is very readily distinguishable, even in the dried animal, and con- 

 tradicts the statement of Mr. H. Goodsir, that they are placed one before the 

 other in the middle of the ventral region (Edin. Phil. Journ. 1842), PI. XXI. 

 fig. 8. 



The internal organs consist of two sets of ovaries placed one on each side, but 

 are not the simple tubes described by VonSiebold ; but as that author's infor- 

 mation consists chiefly of the results of Rathke, Brandt and Miiller, who mostly 

 pursued their researches upon the Isopoda, it may be that still we are both 

 correct in the individual instances. Rousel de Vauzeme figures them in 

 Cyamus ovalis of the same simple character as described by Siebold, termina- 

 ting each posteriorly in a short oviduct. 



The ovaries in Gammarus appeared to us to consist of four or five sac- 

 like organs, narrowing each towards their attachment with a canal into which 

 they all empty themselves in succession, the largest being the most distant 

 from the extremity approximating the vulva. One of these sets was found 

 upon each side of the alimentary canal, and appeared to be enclosed within a 

 common sac; that is, we observed a transparency around the whole organ 

 which induced us so to interpret the appearance, though we were unable to 

 dissect the organ out, or trace it in continuation with the as yet to us undis- 

 covered vulva. 



It is not certain at what time the impregnation of the ovum takes place 

 by the fertilizing spermatozoa, and it is only conjecture that induces us to 

 assume it must be as the former escapes from the oviduct. Thus, if we 

 are correct in our deduction from negative evidence, that an intromission 

 of the male organs does not take place, then we must conclude that the male 

 emission must escape into the surrounding medium, and that of the many 

 thousand active organisms, some are attracted by the force of the continued 

 currents, induced by the swimming feet, into the incubatory pouch, where 

 they are brought into contact with and impregnate the recently deposited 

 ovum, which after fertilization continues in this position to be cherished 

 until after the larva quits the egg. The supposition that impregnation is an 

 external act is supported by the observations of ^'^on Siebold (p. 472 of the 

 work already quoted), that the spermatozoa continue rolled into a figure of 

 8 until they come into contact with the water. 



The Incubatory Pouch is the result of the folding over of several lamel- 

 liform plates, generally fringed with hairs. One of these is developed upon 

 the inner side of each of the two pairs of gnathopoda and the two anterior 

 pereipoda (or four anterior pairs of thoracic feet). These plates overlie each 

 other in a compact form, and securely protect the eggs or the immature 

 young from external accidents (PI. XVIII. fig. 11). 



This lamelliform appendage, which is called the palpe by M. Milne-Ed- 

 wards, is, according to Von Siebold (p. 476), developed at the " epoque du 

 I'ut," and afterwards again disappears. This we have not been able to verify, 

 since we have frequently taken the female at all periods of the year with these 

 appendages fully developed, but do not recollect ever having seen them in a 

 half-formed state. We have never observed them present on the young animal, 

 so that probably they may be produced as the animal arrives towards the 

 era of female development. But we are inclined to doubt, when once deve- 

 loped, that they ever again disappear except as the result of accident. 



