MUSEUM OF COMPARATIVE ZOOLOGY. 497 



of the former, are in error ; the yolk suffers only a minimum contrac- 

 tion, and that occurs in the vicinity of the micropyle. This he has 

 demonstrated also in batrachians and bony fishes. Inasmuch as the 

 peripheral layer of protoplasm adheres in places to the egg membrane, 

 the protoplasm is drawn out, by the invasion of the water, into fine 

 threads connecting the surface of the yolk to the membrane. These 

 ultimately rupture, one end going to form drops on the inner surface of 

 the membrane-, the other, elevations at the surface of the yolk. At the 

 micropyle a much thicker cord of protoplasm — the guiding cord of the 

 spermatozoon (Leitband) — has the same connections. It is through 

 this " Leitband " of protoplasm that the head of the spermatozoon pene- 

 trates to the inner micropyle,^ and thence into the sperm passage, and 

 thus reaches the egg nucleus. Calberla furnishes only very unsatis- 

 factory evidence that the head of the spermatozoon actually advances 

 to the egg nucleus. In sections of hardened eggs he has sometimes seen 

 in the sperm passage an indistinct elongated structure, which he would 

 refer to the head of the spermatozoon. The actual conjugation of two 

 nuclear structures cannot be claimed to have been observed. While a 

 part of the " Mittelstiick " of the spermatozoon may enter the sperm 

 passage, its tail, he asserts, does not enter the egg but remains to plug 

 up the micropyle, and thus prevent the passage of other spermatozoa. 



With the further removal of the egg membrane from the yolk this 

 cord of protoplasm (Leitband) is severed ; its peripheral end forming a 

 great drop on the inner surface of the membrane at the " outer micro- 

 pyle " ; its central end forming a " Dottertropfen " in front of the inner 

 micropyle. Usually this " Dottertropfen " is drawn for a short time 

 within the yolk, only to appear again in consequence of a contractile 

 process within the egg which is connected with a stellar arrangement of 

 the yolk granules. 



Concerning the egg nucleus during the penetration of the sperma- 

 tozoon, Calberla (p. 465) says it is altered, it becomes indistinct, but it 

 does not lose its morphological identity.! It is during this loss of dis- 

 tinct contour that the yolk granules arrange themselves in rays around 

 the disappearing egg nucleus. Subsequently one sees in its place a new 

 nucleus, with sharp contour, which he identifies with Hert wig's " Fur- 

 chungskern.'^ As soon as this segmentation nucleus is formed, the con- 

 traction of the yolk ceases and the "Dottertropfen" retires into the 



* Compare the review (p. 456) of the maturation phenomena as described by Cal- 

 berla for Petromyzon. 



t " Jedoch nicht zu Grunde geht." 

 VOL. VI. — NO. 12. 32 



