DICYEMIDAE ORTHONECTIDAE. 



241 



outer layer of ciliated cells surrounding an inner mass, which in the Dicycmidae 

 consists of a protoplasmic mass with many nuclei, and in the Orthonectidae 

 (single genus Rhopalura) of a mass of cells compacted together. None of them 

 have a digestive cavity. The Dicyemidae are parasitic in the kidneys of 

 Cephalopoda, the Orthonectidae in the gut of Turbellarians, in the body-wall 

 and tissue-spaces of Nemertines, and in the body-cavity and brood pouches of 

 Ophiurids. 



FIG. 193. Rhopalura Giardii. a, male ; ft, cylindrical 

 female of the same (after E. v. Beneden). 



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FIG. 194. Dicycmopsis 

 macrocephalus (after 

 v. Beneden). 



In the Dicycmidae egg- like germs are found in the central plasmic mass which 

 give rise to embryos : no spermatozoa have been found (Fig. 194). In Ortho- 

 nectidae both spermatozoa and ova are found in the central mass, and in different 

 individuals. No light is thrown upon their affinities by their development. 

 The Orthonectidae possess a layer of fibres, presumably muscular, between the 

 outer cells and the inner mass. The males are smaller than the females 

 (Fig. 193) ; and there are two kinds of females the cylindrical forms 

 (Fig. 193, b) and the flattened forms. The history of these forms is obscure. 

 Both forms produce eggs, and are supposed to leave the host to wander into a 



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