PENETRATION AND COPULATION PATHS OF THE SPERMATOZOON 81 



Fertilization of the frog's egg. (A) Sperm penetration and copulation paths in 

 the same direction, forming a straight line, in which case the first cleavage bisects 

 the gray crescent. (B) Sperm copulation path veers away from the penetration 

 path, causing the first cleavage furrow to deviate from bisecting the gray cres- 

 cent. (C) Under compression, the egg protoplasm is re-oriented, and the cleav- 

 age spindle comes to lie in the plane of the longest protoplasmic axis, regardless 

 of sperm activity. (D) Profile view showing sUght movement of the egg nucleus 

 toward the sperm nucleus, after the egg nucleus has given off its second polar 

 body. 



These diagrams are simplified by omitting the changes attending nuclear dis- 

 solution, prior to syngamy. so that the nuclear paths in syngamy can be empha- 

 sized. Only in "A" does the first cleavage coincide with the embryonic axis and 

 bisect the gray crescent. {Solid arrows) Penetration path, gray crescent, embry- 

 onic axis, (broken arrows) cleavage plane, which occurs at right angles to the 

 mitotic spindle. Egg nucleus is clear, sperm nucleus is solid. 



