STRUCTURE AND nF.VET.OPMENT OF COET.OPTANA. 27 



perradial canal (PI. 2, figs. 2, 4; per. r), which forms the trunk of the 

 entire canal-system of each half of the body. The canal is fairly broad 

 but very short; it devides at once into three branches, one which 

 proceeds in the perradial plane and two which lie on each side of it in 

 the interradial plane. The former branch (PI. 3, fig. 2, /. c), the 

 tentacular canal, furcates into two secondary branches close to the 

 proximal end of the tentacle-root which pass along the lateral sides of 

 the latter. Each of the branch is expanded abruptly into a roomy 

 canal at the proximal end of the basis-epithelium, and accompanies the 

 whole extent of the latter (PI. 2, figs. 2, 4, PI. 3, figs. 3-8; t. c). 



The two lateral branch canals of the perradial canal (PI. 2, figs. 2, 

 4; PL 3, figs. 2-5; s. ph. c) run in the interradial direction, traversing 

 obliquely the roof of the pharynx. On reaching just beyond the inter- 

 radial corner of the latter, they bend sharply backwards and pass along 

 the lateral margins of the pharynx towards the sagittal plane of the 

 bod}' and terminate shortly before reaching that plane. These canals 

 without doubt represent the subpharyngeal meridional canals of ordinary 

 ctenophores, and they may be termed the subpharyngeal canals. 



From each furca of the tentacular canal, at about the position 

 where it forms the lateral expansion mentioned before, there arises a 

 canal on the dorsal side (PI. 2, figs. 2, 4; PI. 3, figs. 6, 7, s. t. c). 

 Evidently, this canal is homologous with the subtentacular meridional 

 canal of ordinary ctenophores, and it may be named the subtentacular 

 canal. This canal runs along each side of the tentacle-sheath and 

 terminates a short distance behind the external opening of the sheath. 



Both the subpharyngeal and subtentacular canals give rise to 

 several diverticula on the dorsal side which enter the dorsal tentacles. 

 Further they send off numerous branches on the lateral sides, which 

 undergo divisions and anastomoses and bring about the extensive canalar 

 network in the peripheral parts of the body (PI. 2, figs, i, 2, 4; PI. 3, 

 fig. 2; br. c). The arrangement of the canalar network is subject to 

 considerable individual variation, while the main parts of the canal 

 system keep up constancy in that respect. 



The endodermal epithelium may be divided into three kinds. The 

 first kind is low and cih'ated and consists of cells which are usually flat 

 or cubical and more rarely somewhat cylindrical; further, it comprises 

 so-called ciliated rosettes. This kind of epithelium apparently serves in 

 making water in the canal circulate along through the canal system by 

 means of the activity of the cilia. Further, it seems to absorb nutrition 



