Introduction to Animal Morphology . 107 



under the ridge, as a ctenophoral canal. In some, c. g. 

 Beroe, paragastric and ctenophoral canals open into 

 a circular vessel around the mouth, and the radial 

 canals are obsolete. The whole tubular system is lined 

 by ciliated endoderm. 



Retractile, hollow tentacles exist in Pleurobrachia, 

 one at each side, in sacs about the equator of the 

 body. These are fringed with smaller cirrhi, and 

 here alone thread cells are developed, often in clus- 

 ters. Into these tentacles radial canals extend. The 

 parenchyma consists of connective tissue like that of 

 medusae, and a layer of meridional and transverse in- 

 terlacing muscular fibres lies superficially, which can 

 to some extent alter the body-shape, but does not act 

 in locomotion. In Beroe, lateral secreting organs 

 exist as small bladders, only visible when full ; many 

 such exist in Cestum. 



In Chiajea, Will has described a second vascular 

 system, but this has not been confirmed. 



At the apical pole is a spherical vesicle (ctenocyst, 

 absent in Eurhamphoea), lined by ciliated epithelium, 

 and containing a pigment mass in Bolina, Idya, Pleu- 

 robrachia, and an otolith, to which stiff hairs pass from 

 the epithelium (acoustic hairs). In Eschscholtzia there 

 are two pigment masses beside the ctenocyst. Near 

 this pole also are two oblong apical areas, sur- 

 rounded by branched threads, or covered with hollow,, 

 shaggy processes ; probably areas of sensation, as a 

 nen'e extends to them. 



A ganglion is placed between the apical canals of 

 the funnel, sending off" filaments along the ctenopho- 

 ral ridges, as well as in the wall of the funnel and 

 stomach. Grant describes a circum-oral ring, and 

 something like this is described by Eimer. 



