470 BULLETIN OF THE 



the mass through 90°, whereby each half supplements the half of its 

 own nuclear fluid by the half of that which arose at the opposite pole of 

 the egg. 



In Cephalobus rigidus Butschli ('75, p. 202) says he has seen the 

 process of fecundation in the most satisfactory manner. As soon as the 

 egg reaches the first spermatozoon of the seminal vesicle it unites with 

 it at once. The spermatozoon attaches itself closely to the surface of 

 the yolk, and when the latter has entered the uterus appears already 

 fused with it. The egg certainly combines with no other spermatozoon 

 in its passage through the seminal vesicle. In Cucullanus the egg at 

 the moment of fecundation was not observed, but fecundated eggs dis- 

 closed clearly the entered spermatozoon as a cluster of dark granules sur- 

 rounded hy a dear area. It is therefore not at once fused with the yolk 

 in this case. The results reached in this preliminary account regarding 

 the origin and fate of the pronuclei I have given in connection with the 

 subject of maturation (p. 403). Biitschli fails to connect either of the 

 pronuclei directly with the penetration of a spermatozoon, but attrib- 

 utes the beginning of the maturation phenomena to the influence of 

 fecundation. Since by the ejection of the polar globule a component 

 of the nucleus is removed, it is readily to be inferred that the same is 

 replaced by components of the spermatozoon, especially since subse- 

 quently (during segmentation) a part (spindle) corresponding to the 

 polar globules is found in the nucleus. There is ground for the state- 

 ment that the essential thing in fecundation consists in the removal of 

 the old nucleolus, and the formation of a new one to which elements of 

 the spermatozoon contribute (p. 210). . 



For Bombinator Goette ('75, pp. 51 e^ seq.^ describes the disappear- 

 ance of the germinative vesicle, which leaves behind for some time a 

 starlike figure in the upper half of the yolk. Immediately after fecun 

 dation in the more advanced eggs, a "yolk nucleus " (Dotterkern) has 

 already made its appearance near the middle of the egg as a large, 

 round, somewhat flattened body, with distinct but not sharp contour. 

 The finely granular substance of the disintegrated germinative vesicle 

 reaches within its territory, but with such want of uniformity as to 

 justify the assumption that the two structures sustain only a chance 

 relationship. This " Dotterkern " migrates toward the upper pole of 

 the egg, while the discoloration of the yolk, due to the disintegration of 

 the germinative vesicle, disappears entirely ; and thereupon is formed 

 within it a delicate round corpuscle — the first " Lebenskeim " — which 

 induces the further development of the egg. This " life germ " per- 



