BLACKMAN : THE SPERMATOGENESIS OF SOOLOPENDRA. 87 



lead to conclusions like my own. In well-fixed and well-stained prepara- 

 tions of S. heros no other conclusions than those I have presented seem 

 possible, and I believe that the same is true of S. dalmatica. The ap- 

 parent disappearance of this element in the late prophase can also he 

 very easily explained. The "nucleolus," bereft of the material going to 

 form the ordinary chromosomes, is now identical with its condition be- 

 fore the vesicle stage, i. e. it is again merely the accessory chromosome, 

 and is so closely similar to the other chromosomes of this stage that it 

 can be distinguished from them only in very favorable material. 



By the great majority of investigators of amphibian ova it is agreed 

 that at certain periods in the development of the egg the chromatin is 

 either entirely — Schultze, '87 (Rana and Triton) ; Carnoy et Lebriin, 

 '97, '98, :00 (Amphibia) — or at least partially — Macallurn, '91 (Rana 

 and Xecturns) ; Jordan, '93 (newt) 1 ; Fick, '93 (Axolotl) — collected 

 in the form of a number of nucleolus-like bodies. The observations of 

 several other investigators — Metzner, '94 (Salamandra) ; Eisen, :00 

 (Batrachoseps) — upon spermatogenesis in Amphibia would indicate that 

 similar phenomena sometimes occur in the male germ cell as well ; and 

 the works of Rabl, '85 (Salamandra), and Lavdowsky, '94 (Amphibia) 

 would indicate that the somatic cells of larvae behave in a similar 

 manner. From these observations there can be no doubt that in numer- 

 ous cases the chromatin reticulum of Amphibian cells is wholly or 

 partly broken down and becomes aggregated into a large number of 

 pseudo-nucleoli. 



A similar process also undoubtedly occurs in the germ cells of Mas 

 according to the observations of Hermann ('89), Holl ('93), and Sobotta 

 ('95). Hermann, working upon mouse material, reports nucleoli com- 

 posed of chromatin as present in the cells at various stages of spermato- 

 genesis. In the spermatid there are at first several, but later these fuse 

 to form a single large one. Holl reports that in the germinative vesicle 

 of the mouse ovum there is a large nucleolus composed chiefly of chro- 

 matin, from the substance of which the chromosomes are derived during 

 the prophase of the first maturation division. Sobotta states that dur- 

 ing fertilization stages the pronuclei, both male and female, contain 

 generally one but often several large nucleoli, which under the highest 

 powers appear to be homogeneous masses of pure chromatin. " Der 

 ganze librige Kern reprasentirt nur ein achromatisches Kerngeriist." 



1 The nucleolus in this material is derived from the reticulum of the nucleus, 

 but at the same time is said to take no part in the subsequent formation of the 

 chromosomes. 



