142 



BERTRAM G. SMITH 



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44 



45 





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46 



47 



48 



Fig. 44 Vertical section through an egg of Cryptobranchus allegheniensis 

 killed 1\ hours after fertilization, showing a late stage in the penetration by the 

 spermatozoon. X 80. This spermatozoon has entered the egg about 30° from the 

 animal pole, and its path inclines toward the axis of polarity of the egg. The head 

 of the spermatozoon is shown entire; the tail persists in an abbreviated and 

 perhaps fragmented condition, but does not appear in the section figured. An 

 aster is present in an adjacent section at a little higher level than the sperm head. 

 Another spermatozoon in the same general condition is found in the same egg. 



Fig. 45 Vertical section through an egg killed IO2 hours after fertilization, 

 showing the sperm-nucleus. X 80. The spermatozoon has entered the egg about 

 25° from the animal pole. Fragments of the tail of the spermatozoon are to be 

 found in the vicinity of the sperm-nucleus, but are not shown in this section. 



Fig. 46 A portion of fig. 45 enlarged to show the sperm-nucleus. X 240. 



Figs. 47 and 48. Two consecutive meridional sections through an egg of Crypto- 

 branchus allegheniensis, killed 10§ hours after fertilization, showing the egg- 

 nucleus. This nucleus is situated about one-third as far from the surface as the 

 copulation-nucleus shown in fig. 52. X 240. 



