NATURE AND ORIGIN OF THE GERM-CELLS 39 



several nucleoli. As they are very variable and often tran- 

 sient, the nucleoli are not regarded as very important. Often 

 they seem to be aggregations of reserve material or of waste- 

 products. 



The Typical Spermatozoon. — The germ-cell produced by the 



i (/ //I/)/ ii, , 



t/l/iAu^^ 



Fig. 7. — Volvox globator, an Infusorian forming a colony of cells, 

 showing the ordinary cells (c) that make up the colony or incipient 

 " body " ; a and b, the special reproductive cells, both male and 

 female — the beginning of the distinction between germ-cells and 

 somatic cells. 



male parent, the spermatozoon, is very different from the ovum 

 in appearance and structure, and is also very much smaller. 

 When the e^^ is swollen with yolk, which does not count as living 

 material, the spermatozoon may be less than a millionth of its 

 volume. Most of the cytoplasm of the spermatozoon forms a 

 locomotor flagellum or tail, often of intricate structure, which 

 drives the " head" or nucleus before it, always working against 



