144 



MANUAL OF ZOOLOGY. 



and wider cavity (c), termed the " funnel," from which two 

 canals diverge in the direction of the vertical axis of the 

 organism, to open at the " apical pole." These canals are 

 known as the " apical canals " (e), and their apertures as the 

 " apical pores." From the funnel two other pairs of canals are 

 given off. Of these, one pair known as the " paragastric 

 canals " turns upwards, one running parallel to the digestive 

 sac on each side (d), and " terminating caecally before quite 

 reaching the oral extremity." The second pair of canals (/) 

 the so-called "radial canals" branch off from the funnel 

 laterally, each dividing into two, and then again into two, as 

 they proceed towards the periphery of the body. Thus, the 

 two " primary " radial canals produce four " secondary " 

 canals (/), and these, in turn, give rise to eight " tertiary " 

 radial canals (/), which finally terminate by opening " at 



Fig- S3- Morphology of Ctenophora. i. Diagrammatic transverse section of Pleu^ 

 robrachia, b Digestive cavity ; i i Primary radial canals ; k k Secondary radial 

 canals ; / / Tertiary radial canals ; Tentacle. 



2. Longitudinal section of P leurobrachia. a Mouth ; b Digestive cavity ; e Fun- 

 nel ; d d Paragastric canals ; e e Apical canals ; f Ctenophoral canal ; g Tentac le ; 

 h Ctenocyst. (After Greene.) 



right angles, into an equal number of longitudinal vessels, the 

 'ctenophoral canals' (/), whose course coincides with that 

 of the eight locomotive bands. These canals end caecally 

 both at their oral and apical extremities " (Greene). The 

 whole of this complex canal-system is lined by a ciliated 

 endoderm, and a constant circulation of the included nutrient 

 fluid is thus maintained. 



Immediately within the apical pole is situated a small cyst 

 or vesicle, supposed to be an organ of sense, and termed the 

 " Ctenocyst " (h). In structure the " ctenocyst " consists of a 

 spherical vesicle, lined with a ciliated epithelium, and filled 

 with a clear fluid, which contains mineral particles, probably 

 of carbonate of lime. Resting upon the ctenocyst is a small 

 ganglionic mass, giving origin to a number of delicate filaments, 



