2Q4 ENTOPROCTA. 



During the completion of the alimentary canal a number of 

 important structures is formed. The disc in which the oral and 

 anal apertures are situated becomes converted into a true vesti- 



FlG. 129. TWO STAGES IN THE DEVELOPMENT OF PEDICELLINA. (After 



Hatschek.) 



oc. oesophagus ; ae. archenteron ; au.i. anal invagination ; f. fold of epiblast ; 

 f.g, ciliated disc ; x. problematical body derived from hypoblast (probably a bud). 



bule. On its floor, between the mouth and the anus, there arises 

 a marked prominence with a tuft of cilia (fig. 130 B), which 

 persists in the adult. 



This prominence is perhaps equivalent to the epistome of the 

 Phylactolaemata and the disc-like organ of Rhabdopleura, which 

 Lankester has compared to the molluscan foot 1 . 



Very shortly after the first formation of the vestibule there 

 appears at the opposite end of the larva a thickening of the 

 epiblast, which soon becomes invaginated, and forms an eversible 

 pit (fig. 129 A and B, f.g.). Round its mouth there is formed a 

 ring of stiff cilia (fig. 130, f.g.}. This organ is very possibly 

 equivalent to the cement gland described by Kowalevsky in the 

 adult Loxosoma. I shall speak of it as the ciliated disc. 



The epiblast cells early secrete a cuticle. 



The two mesoblast cells soon increase by division, and 

 occupy the space between the alimentary canal and the body 

 wall. They do not become divided into a splanchnic and 

 somatic layer ; but give rise to the interstitial connective tissue 



1 Lankester. "Remarks on the Affinities of Rhabdopleura. 1 ' Quart. J. of 

 Micro. Science, Vol. xiv. 1874. 



