308 THE STUDY OF ANIMAL LIFE CHAP, xiv 



spermatozoon to a minute monad Infusoriaii. It is a 

 very small cell, bearing at one end a " head," which con- 

 sists mostly of nucleus, prolonged at the other end into 

 a mobile "tail," which lashes the head along (fig. 102). 

 Between the ' head ' of the spermatozoon and the 

 " tail ' there is a little connecting piece, or " middle 

 piece," and in this lies a minute body the centrosome, 



FIG. 101. THE MALE-CELL OR SPERMATOZOON OF A CRAYFISH. 



In most Crustaceans the spermatozoa are sluggish and give off radia- 

 ting locomotor processes (P). They are quite unlike typical spermatozoa 

 which have a small head containing the nucleus and a relatively long 

 locomotor tail. In most Crustaceans, as in the crayfish, lobster, and 

 crab, the spermatozoa are deposited upon the eggs. The nucleus (A') is 

 seen surrounded by more cytoplasm than is usual in a spermatozoon. 



which is introduced by the spermatozoon into the egg and 

 plays an important part in the divisions which follow 

 fertilisation. 



In the history of the spermatozoa within the testis, 

 a number of primitive sperm-cells (spermatogonia), 

 which should be compared to the primitive egg-cells 



