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 



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 egg 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 



