21 



offering special advantages for undertaking this investigation on 

 account of the abundance of materials it commands. The same subject 

 has been worked over by E. Verso n and described in two papers, 

 »La spermatogenesi nel 5. mori, L.«, Padova, 1889, and »Zur Sperma- 

 togenesis« in this journal, XII. Jahrg. 1889. 



The testes of the silkworm are kidney-shaped and being paired 

 lie right and left over the alimentary canal , in the segment where the 

 sixth stigmata open. Each testis, as Ver son has already mentioned, 

 consists of four conical blind tubes or testicular follicles and lies 

 embedded in a common envelope, Tunica adventitia. 



Even in the first larval stage , where the sexual differentiation of 

 germ cells is not yet to be noticed, the difference of the shape of sexual 

 glands is to be seen: the male gland is kidney-shaped while the female 

 gland is triangular and smaller. Moreover, the vas deferens is found 

 on the inner side of the male gland while the oviduct is attached to 

 the outerside of the ovary. 



The development of the genital elements. 



On examining under a microscope the testis of a larva after the 

 fourth moult, we are struck with varieties of cellular elements found 

 in it. Near the blind end of each testicular follicle, we find a large 

 cell around which small cells are arranged concentrically. 



Before proceeding to describe the development of the genital ele- 

 ments , I shall say a word or two as to the nature of this large cell in 

 the blind end. 



Ver son' s interpretation of this cell is as follows: »In jedem Fache 

 befindet sich nun eine einzige, große Keimzelle, und aus dieser neh- 

 men nach und nach alle organisierten Bildungen ihren Ursprung, aus 

 welchen der Inhalt des ganzen Faches besteht.« 



In the embryonic stage, each of the paired genital glands of both 

 sexes consists of only one cavity but as the development proceeds, 

 three slight depressions appear in the follicular wall. These deepen 

 until the genital gland shows four deeply cut lobes. When the first 

 three depressions deepen a little , four new invaginations of the folli- 

 cular wall appear in each of these lobes. Into each of these new de- 

 pressions , a follicular cell enters , which soon enlarges and loses its 

 cell-wall. The genital elements already present now arrange them- 

 selves around this follicular cell and in later stages it is clearly to be 

 seen that there is a protoplasmic communication between this inva- 

 ginated follicular cell and the genital cells. I have never found, as 

 Ver s on states, this central cell in the state of division in tracing it 



