5. The morphology of Duplorbis and the derivation of the endoparasitic development. 



61 



body, exhibiting the mesenteric canal (mes.can. in red) in all its length, opening posteriorly 

 at the summit of the peduncle (ped), and anteriorly into the mantle-cavity (be) just behind 

 the nervous ganglion (gn). 



Text fig. 1 is a morphologically transverse section, and here the mesenteric canal (tnes. 

 can, in red) is shown as a tube lying in the mesentery (mes). This canal is lined throughout 

 with chitin, which is continuous with the chitinoxis layer of the external surface of the body 

 and of the internal surface of the mantle-cavity; the canal exhibits a regular epithelium, 

 but no glandular appendages. It is surrounded by the lacunar tissue of the mesentery and evi- 

 dently represents the organ by which the parasite absorbs its nutrition from the host. 



A superficial interpretation of this tube might lead us to regard it as a gut, the mouth 

 being at the summit of the peduncle and the anus at the opening into the mantle-cavity, but 

 the reader will hardly adopt, nor would I encourage an interpretation so utterly at variance 



7n.es. cam. 



Vi.sc 



•mc 



meS. ccun, 



vtir 



J»VC 



Text fig. 17. 



with all we know of ('impedes in general, and of the Rhizocephala in particular. Cirripedes 

 do not fix themselves by the mouth, but by the antennae which become converted into the 

 stalk, and the Rhizocephala never possess a mouth or gut even as larvae, and their fixation is 

 always accomplished by means of the antennae as in all other Cirripedes. 



What then is the morphological nature of the mesenteric canal in Duplorbis? 



It represents, in my opinion, the invaginated stalk of an ordinary 

 Cirripede. 



