174 



EARTHWORMS. PHYLUM ANNELIDA 



gradually increase in length, and change their shape till the mul- 

 berry has become a tuft of threads, each thread being a sperma- 

 tozoon with a very slender head. Finally the spermatozoa break 

 loose. In the median part of each seminal vesicle, directly behind 



Fig. 123. — The development of the spermatozoa of the earthworm, 



^.Stages from the vesicula seminalis of a young worm ; B, from that of an older worm. 

 1, bperm rnothor-r.f>ll ; 2-7. stages in the division to form spermatozoa ; 7-11, shaping of the spermatozoa, 

 ^' t to the mass of residual protoplasm (cytophore) ; 12. a ripe spermatozoon, 



_^ "'' . 12 is represented rather too broad. 



The «iaik uudics cuc Itic nuclei, stained. 



