Chap. XIII.] 



SPERM A TOGENESIS. 



479 



We must first develop in detail the characters of the 

 parts whose general morphology has just been 

 sketched. 



It is only lately that much attention has been 

 given to spermatogeiiesis, or the history of the 

 development of the spermatozoa, and it will be most 

 convenient, therefore, to give an account of a common 

 form (the earthworm) in which the process seems to 



B 



Fig. 203. Figures showing the Mode of Development of the Sperma- 

 tozoon of the Earthworm. A, Spermatospore ; B, ?oung Sperma- 

 tosphere, with eight Spefmatoblasts ; c, Spermatoblasts with 

 Central Blastophore ; D, Spermatoblasts with protruding Filament 

 (After J. E. Blomfield.) 



have been worked out (by Blomfield) with great 

 exactness. 



The testis of the earthworm is a body of irregularly 

 quadrate form, which is about one-tenth of an inch in 

 diameter, and is directly attached to, and seems to 

 form a modified part of, the epithelium lining the 

 body cavity ; it consists of a mass of cells, each of 

 which, breaking away from the common mass, makes 

 its way into a special reservoir, there to undergo its 

 further development. Each of these cells may be 

 known as a spermatospore, and is distinguished 

 by the comparatively large size of its nucleus, and its 

 thin coat of surrounding protoplasm ; the nuclei of 

 these spermatospores undergo division, and the whole 

 mass increases in size. When eight segments have 

 been thus formed we get the spermatosphere, 



