ORTHONECTID^ AND DICYBMID5; 



207 



order to seek a new host. In the body cavity of the latter, 

 again an Amphiura, their life-history is continued, but in a 

 different manner in the two forms. The flattened females 

 are said by Julin to break up into a number of fragments, 

 each one of which is composed of several central and peri- 

 pheral cells. These ciliated offspinng develop into the 

 "plasmodial sacs" of Metschnikoff (No. 6). These are 

 sac-like structures, which consist of a granulated mass, and 

 exist in large numbers within the body cavity of Amphiura 

 and Nemertes. The centi^al cells contained in them are to be 

 considered as eggs, and 



(in consequence of a A ^* li'i' ^ 



kind of parthenogenetic 

 reproduction) supply 



both forms of females. 



The cylindrical females 



while still in their new 



host expel their central 



cells — i.e., the eggs — and 



these develop into in- 

 dividuals which differ 



considerably in shape 



from the females already 



described. They are the 



males of Rhopalura Giar- 



dii, which, according to 



Julin, are brought forth 



by the cylindrical 



females only. Whereas 



the body of the female 



is segmented externally 



into nine rings, there are 



only six rings in the male (Fig. 97 B). The second ring, 



as in the females, is without cilia. The five rows of cells 



which constitute it contain peculiar highly refractive bodies. 



Within the animal there is differentiated an oval, sac-like 



organ of a granular appearance. From it fine cords, which 



are interpreted as muscle fibres, extend in the body forward 



and backward. The organ itself corresponds to the testis ; 



Fig. 97.— .1, cylindrical female; B, male 

 of Rhopalura Giardii (after Julin); H, testis ; 

 M, muscle fibres. 



