VII 



MOLLUSC A PARASITIC GASTROPODA 



247 



false mantle becomes larger and larger, and envelops the small visceral dome, which 

 gradually becomes rudimentary, and finally contains merely the genital organs. At 

 the stage D the whole animal already projects freely into the body cavity of the 

 host, attached to its wall by a displaced portion of the false foot, and connected with 

 the exterior only by the aperture of the false mantle. If this last means of 

 communication with the exterior is also abandoned, i.e. if the whole false mantle 

 with its aperture becomes enclosed in the body cavity of the host, we have a form 

 corresponding with the endoparasite Entocolax Ludwigii (Fig. 205). In this form, 

 the cavity enclosed by the false mantle, into which the ovary and its receptacula 



FIG. 206. 



-m, 



FIG. 20 



FIG. 205. Entocolax Ludwigii, sketch 

 after Voigt. Lettering the same as that in 

 the preceding figure. 



FIG. 206. Entoconcha mirabilis, sketch 

 by Schiemenez (after Baur). Lettering as 



in Fig. 204. liod, Testes? 



seminis open, serves as a receptacle for the fertilised eggs, which were found in it in 

 their first stage of segmentation in the one (female) specimen discovered. 



Entoconcha mirabilis, an endoparasite which has been found in a Holothurian, 

 Synapta digitata, is even more deformed than Entocolax. The body of this parasite 

 is a long vermiform coiled tube, attached by one end to the intestine of the host, 

 while the rest of the tube floats freely in the body cavity of the latter. Its 

 organisation has as yet been imperfectly investigated. Fig. 206 is a very simple 

 diagram, which is introduced for comparison with Fig. 205 of Entocolax. It is 

 impossible to say how far such a comparison, which the lettering is intended to 

 facilitate, is justifiable. Up to the present time, no aperture leading from the ovary 

 into the brood-chamber, which is thought to be the cavity of the false mantle, and is 



