138 



ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



result being a large number of small rounded blobs of cytoplasm each 

 containing a nucleus and all connected together by a common mass of 

 protoplasm in the centre. The central cytoplasm has increased much 

 in size and forms a large spherical mass the surface of which is covered 

 by the little round masses already mentioned so that the whole looks 

 like a minute raspberry or mulberry. This stage is the sperm-morula 

 referred to on p. 52 (see Fig. 21, A). With further development the small 



S.U.1L 



n.o. 



Fig. 67. 



Lumbricus. Plan of genital organs, nephridia. etc. c.f, Coelomic funnel of male genital duct ; 

 rt, nephridium ; n.c, nerve-cord ; n.o, external opening of nephridium ; ns, nephrostome ; od, 

 coelomic funnel of oviduct ; ov, ovary ; sp, spermathecae ; s.vj., anterior seminal vesicle ; s.v.ll., 

 posterior seminal vesicle ; t, testis ; v.d, vas deferens. 



rounded bodies become pear-shaped^ their outer ends becoming pointed. 

 Later on they become drawn out into fine filaments, the inner thicker 

 portion composed of the condensed nuclear material, the outer composed 

 of cytoplasm highly contractile and capable of active flexure from side 

 to side. Finally they break off as complete microgametes or spermatozoa 

 and swim actively by the movements of their contractile '' tails." 



The spermatozoa like the eggs lie in the cavity of the coelome but, 

 in correlation with their small size and active movements, they are 



