762 MURIEL ROBKUTSON. 



F'l'^. 21.— Still later stage; some of the nuclei appear to be preparing 

 for division. 



Fitr. 22. — Multinucleate scliizont cut across in section. 



Fig. 23.~Late stage of schizogony in lung, the protoplasm beginning 

 to segregate round the nuclei. 



Fig. 21.— Fidly formed merozoites ; only a very few of the t(jtal 

 number formed are sliown in the section. 



Figs. 25—56 represent stages in the leech Ozobranchus shipleyi 



Harding. 



Figs. 25 and 26. — Non-motile stages from the crop. 



Fig. 27. — Degenerating stage from the crop. 



Fit's 28-32. — Free motile stages in the lumen of the intestine of the 

 leech. 



Fiss. 33-37.— Association in the lumen of the intestine. 



Figs. 38-41. — Early stages in tiie cells of the intestinal wall. 



Fiir. 42. — Precocioxis dift'ei-entiation of microgauiete. 



Fig. 43. — Early stage of niacrogamete. 



Figs. 44 and 45.— Stages suggesting conjugation. In fig. 44 the 

 uiicrogametocyte is lying closely applied to tiie macrogamete. In 

 tig. 45 the uiicrogametocyte appears to Ik- giving rise to the micro- 

 •••amete nuclei, one of which will fuse with the nucleus of the macro- 

 gamete. 



Fig. 46.— Early stage of spovocyst showing two nuclei. 



Fig. 47 —(A) Stage apparently representing a zygote; (b) stage show- 

 ing what appears to be tiie first division of the zygote nucleus; (c) free 

 sporozoites in the wall of the intestine. 



Fig. 48. — Stage of above showing five nuclei, of whicli one is prepar- 

 ing to divide. 



Fig. 49. — Sporocyst with eight nuclei : the protoplasm has not yet 

 divided up ; the rejected microgamete nuclei iire still visible. 



Figs. 50-53.— Sporocysts showing sporozoites. 



ri«^^s. 54 and 55. — Motile spoiozoites escaping througli the cells of 

 the intestinal wall. 



Fig. 56. — Sporozoite in blood-space of the leech. 



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