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 Jsopoda is very similar; but 
M. Lereboullet has failed to trace the connection of the 
ovaries with the vulva. Herr Schobl 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 receptacule seminales, in which the male animal 
deposits the spermatozoa that fructifies the ovee. 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 coxe 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, 
