SYNGAMY 



is the union of fully-grown adults, but in other such creatures 

 (Fig. 8), and in all large and complex animals and plants, 

 syngamy takes place only between the reproductive bodies, 

 which are generally unable to develop without it, so that it 

 becomes a necessary part of the reproductive process. In these 



creatures the reproductive 

 bodies are of a kind known 

 as germ cells, distinguished 

 from other reproductive 

 bodies (free buds, etc.) by 

 their small size and the sim- 

 plicity of their structure. 

 The germ cells of such 

 creatures are usually of two 

 sizes which unite larger with 

 smaller (Fig. 8C). In all 

 large and complex animals 



Fig. 3. — Heads of human spermatozoa, in side and face view. Electron photo- 

 micrographs. The scale is one micron. — From Friedlander Proc. roy. Soc. B., 

 1952, 140. 



(and in some of the smallest) the gametes differ in form and 

 behaviour as well as in size (Figs, i and 3). One is larger and 

 passive, and is called the female gamete, or, in large animals, the 

 egg or ovum. The other is smaller and active, and known as 

 the male gamete or spermatozoon or sperm ; it has usually a tail 

 (flagellum) with which it swims in the fluid in which it is borne, 

 and thus it moves to the e^g and enters the latter (Fig. 4). This 

 process is known as the fertihsation of the ovum. After it the 

 fertilised ovum proceeds to develop. Ova and spermatozoa are 

 usually formed by different adults, known respectively as female 



