xlii INTRODUCTION. 



According to the former authors, corroborated in part 

 by Mr. H. Goodsir on the genus Caprella, by Roussel de 

 Vauzeme on Cyamus, and from our own direct observa- 

 tion on Gammarus, &c., the internal organs consist of 

 two sets of ovaries. These are long cylindrical bodies, 

 having a duct near the middle, on the inner side, that 

 opens into the vulva, which is situated on the inner side 

 of the coxa of the third pair of pereiopoda, or fifth pair of 

 legs. According to the latter authors, the structure of 

 the same organs in the Isopoda is very similar ; but 

 M. Lereboullet has failed to trace the connection of the 

 ovaries with the vulva. Herr Schb'bl has been more suc- 

 cessful in his researches on the genus Typhloniscus, and 

 has figured them attached to the inner surface of the 

 fifth pair of legs. He has also described and figured a 

 pair of receptaculce seminales, in which the male animal 

 deposits the spermatozoa that fructifies the ova3. Accord- 

 ing to this statement, in the Isopoda, if not in the Amphi- 

 poda also, the male impregnates the female by direct 

 intromission a circumstance of which we have entertained 

 some doubt, partly arising from the formation of the 

 animals themselves, particularly of the Amphipoda, in 

 which the development of the coxa3 and the narrowness 

 of the animal would almost, it would seem, preclude the 

 possibility of the sternal portions of the animals being 

 brought into immediate contiguity, and also from the 

 circumstance of having watched the animals, particularly 

 Asellus, from previous to impregnation to the birth of 

 the young, we have never seen the male in any position 

 relative to the female except in that previously described. 



The incubatory pouch, in which the ova are deposited, 

 from the period of their fertilization until the young are 

 developed sufficiently for independent existence, is the 

 result of the folding over of several lamelliform plates, 



