60 



The Endoparasitic Development of the Rhizocephala. 



as to prevent one more moult, and this moult which brings the reproductive part of the 

 parasite to the exterior is the final growth-effort of the host, which henceforth remains 

 without an ecdysis until the death of the parasite. In this remarkable manner the host is 

 compelled to act in a way serviceable to its enemy. 



In the next section the derivation of the endoparasitic development will be further 

 considered. 



5. The morphology of Duplorbis and the derivation of the 



endoparasitic deyelopment. 



It seems probable that the condition and manner of fixation in Duplorbis calathurae, 

 the parasite of the Isopod Calathura orecchiata which is described in detail on pp. 120 — 122, 

 may throw a considerable light on the steps by which the endoparasitic development of the 

 other Rhizocephala has been attained. 



Without entering into the details of the anatomy of this animai which will be found 

 in the Systematic part I will here explain its apparent manner of fixation on its host, and 

 the relation which this manner of fixation may bear to the general problem of Rhizocephalan 

 development. 



The only three specimens of Duplorbis so far discovered, were found by Dr. Hansen on 

 a single specimen of Calathura brachiata in the position shown on Piate 8 fìg. 9. Each specimen 



„.-nejoL 



ytìjL-s. cam. 



m 



7ne.S.can\ 



insc 



Textfig. 15. 



Text fìg. 16. 



Tnes 



•A,--. •„-,-,•. •-. ■ > .l. 



J\ùli JfC 



was fixed to the abdomen of the host by means of a peduncle which penetrated the external 

 tissues of the abdomen. Apparently no roots are given off from this peduncle, but a tube 

 is present opening at the top of the peduncle into the body of the host and running in the 

 substance of the mesentery to open into the mantle cavity of the parasite. The relations of 

 this tube, which I cali the mesenterio canal, are shown in the diagrams Text figs. 15 and 16. 

 Text fig. 15 represents a section taken through the morphological long axis of the 



