SPERM ATOGENESIS—INSEMIN ATION 



175 



sperms are said to be amcEboid. In some crustacean sperma- 

 tozoa there are a number of radiating spine-like processes 

 whicli seem to take the place of the flagellum. 

 r In other animals, and notably in the gasteropod mollusc 

 Paludina, there are two kinds of spermatozoa. In this animal 

 one is of the usual type, whereas the other is larger and worm- 

 shaped, with a tuft of ciUa at one end. The smaller variety 

 alone is said to be functional.^ 



The size of the sperm varies greatly in different animals. 

 In Man its length is about -05 millimetres or a 300th of an inch, 



fi 



a 



d 



/ 



9 



Fig. 48. — Different forms of spermatozoa from different species of animals, 

 as follows : — 



a, bat ; i & c, frog ; d, finch ; e, ram ; f k g, boar ; /i, jelly-fish ; 

 i, monkey ; Tc, round worm ; I, crab. (From Verworn.) 



the head and the middle-piece being each about -005 millimetres 

 long. 



It is obvious that the sperm contributes comparatively httle 

 material to the fertiKsed ovum, being provided with only suffi- 

 cient protoplasmic substance to form a locomotive apparatus 

 by means of which it gains access to the ovum. The pre- 

 dominantly destructive metaboHsm of the spermatozoon as con- 

 trasted with the ovum has been strongly emphasised by Geddes 

 and Thomson,^ who believe it to exemphfy those kataboUc 



1 For further details of the structure of various kinds of sperms see 

 Wilson, loc. cit.; also Ballowitz's papers just referred to, and Retzius' 

 Biologische Untersuchungen, vols, xi., xii., and xiii., Stockholm and Jena. 

 The latter contains numerous large plates with figures of spermatozoa. 



- Geddes and Thomson, The Evolution of Sex, Revised Edition, London, 

 1901. 



