72 



GENERAL PRINCIPLES OF ZOOLOGY 



germinal vesicle always occurs in the egg. Its contents are mainly the 

 nuclear fluid, ihrough which is distributed an achromatic network, and 

 in addition the nucleolus (germinal spot). 



The Spermatozoa, the morphological elements of the male reproductive 

 product, are so small that their liner structure can be studied only with the 

 strongest powers of the microscope (lig. 37, I and II). Easiest to rec- 



ognize is the head, wh'ch from its form— spherical, oval, sickle-shaped, 

 etc. — often renders possible the speciiic determination of the spermatozoa. 

 The head (2) is the closely compacted chromatic part of the nucleus, and 

 hence colors very deeply in staining fluids. Often the head is continued 

 in front as a sharp point, the pcrforaioriiim (t), which is apparently 

 adapted to aid in the penetration of the egg in fertilization. Next comes 



