INTERNAL ANATOMY OF THE GAMASIN^. 293 



tlie mode of development in the Crayfish, is that of Gam.asus crassus, Kramer ; at least 

 I believe that this is the species, but as there is a little difference in the epistome from 

 his figure, I have drawn that organ and the mandible of the male (PL XXXII. figs. 20, 19)*. 



The process of development in this species is delineated by fig. 35 ; the different 

 stages are numbered successively ; it commences with a single very minute cell (1), 

 Avhich gradually enlarges until tlie nucleus can be clearly seen (2) ; this then divides 

 into two (3), then into four (4), eight, &c., in the ordinary manner, the cell continuing 

 to enlarge all the time, so that each contained S2)here, after numerous divisions, is as 

 large as one of the original two spheres. In this manner a small nuclear-aggregate 

 (Winkler's "Morula von Kernen ") is formed inside and detached from the peripheral 

 protoplasm (5). So far, of course, there is not anything unusual ; but now commences 

 Avluit strikes me as singular : the whole cell becomes slightly flattened and more 

 discoidal ; four, or more rarely three, slight rounded projections apjiear on the margin 

 at equal distances (6); these projections continue to increase in length (7), and this 

 goes on until the whole thing presents curiously the form of au Ophiocoma, except 

 as regards number of rays (8). The contained spherules arrange themselves chiefly in 

 the arms, and either break up or are no longer distinctly visible ; an indentation appears 

 in the edge of the disk between each two rays, which deepens until the four rays are 

 only joined by their points (9). In this manner each ray has become a long tubular 

 spermatocyst with a slightly clavate head ; this head, however, becomes indented on 

 one side, and the inner end bends outward so as to form a hook (10). This stage is 

 interesting because it is the permanent form of the spermatocysts, or spermatozoa, 

 in some other species, e. g. Sejus togatas (see PI. XXXIII. fig. 45, which represents a 

 group taken from the testis of the female in that species ; those from the spei-matheca 

 are similar). Pinally the hooked end straightens out; both ends of the cell become 

 pointed, and the whole cell might then, as far as appearance is concerned, well be a single 

 spermatozoon were it not for its size (11) ; it is in this form that it is found in the vasa 

 deferentia ; I am not sure that it docs not split longitudinally into two spermatozoa. 

 Certainly the single semen, be it spermatozoon or spermatocyst, is often very much finer 

 a)id thinner even than 11 ; it becomes quite filamentous, particularly those found in the 

 female and capsule (see explanation of the word " capsule " in the part on the mode of 

 copulation). I think these filaments are the mature spermatozoa. 



Before closing this section it is perhaps well to refer to what Winkler says of the 

 spermatogenesis in G. o-assipes, in order that by describing the whole process for the 

 sake of clearness I may not be suj^posed to claim the discovery of anything which he 

 has already observed. 



The spermatophores, as he finally calls them, are smaller in his species than in many 

 others, and I believe his description to be quite correct. He says that the primary cells 

 divide and form daughter-cells ; tlie nucleus of the daughter-cell divides frequently and 

 becomes what he terms a morula within an envelope or cyst (Umhiilluug); the divided 

 nuclei arrange themselves in a strip ; the cell becomes clavate, then lengthens out, Init 



* Prof. Berlese says that this species is identical -with G. coleoptratorwii ; but this is an error on the Italian 

 Professors part ; the two species are very different. 



