Ill 



SYNGAMY 



75 



centrosome soon becomes visible in the middle piece, and an astral 

 radiation appears round it. It next divides into two (if it has not already 

 done so in the spermatid), a spindle figure being spun out between the 

 two daughter centrosomes, and thus a complete achromatic figure is 



^» '<:'' 



■f ^ 

 # 



/ 



1^ 



D 



:/. 



'it- 



Fig. 34. 



Syngamy in various animals. \, Physa fonlanalis (after Kostanecki and Wierzejski, A.m. A., i8g6) just 

 after entry of spermatozoon ; B, the mouse (after Lams and Doorme, A.B., 1908) spermatozoon in the act of 

 entering the egg ; C, D, successive stages in the fusion of the gamete nuclei in Ophryotrocha puerilis (after 

 Korschelt, Z.w.Z., 1895) ; E, F, the penetration of the amoeboid spermatozoon in Ascaris canis (after Walton, 

 J.M., 1918). 



c, centrosome in middle piece ; h, head ; /, tail of spermatozoon. 



formed under the influence of the sperm centrosome. This is the 

 achromatic figure of the zygote nucleus, for after the formation of the 

 second polar body the entire achromatic figure of the egg, including the 

 centrosomes, disappears. Thus the centrosome, and hence the whole 

 achromatic figure of the zygote, is entirely derived from the spermatozoon. 

 This conclusion is based on numerous observations, and also is well 



