146 MANUAL OF ZOOLOGY. 



4. The " ctenophoral system," consisting of the tubes which 

 run underneath the locomotive bands. 



In Beroe, which is in other respects very similar to Pleuro- 

 brachia, the axial system of canals is the same as we have seen 

 in the latter. The paraxial system, however, consists of two 

 pairs of paragastric canals, which, instead of terminating 

 caecally, open into a circular canal which surrounds the mouth. 

 The ctenophoral canals, likewise, open into the oral vessel, 

 instead of terminating caecally as in Pleurobrachia. Lastly, 

 the radial system is not developed, the ctenophoral canals 

 simply curving round towards their apical extremities, and 

 opening into the funnel directly. 



Amongst the Beroidcz the mouth extends entirely across the 

 oral extremity of the body; hence they have been termed 

 Eurystomata, the term Stenostomata being applied collectively 

 to all the other Ctenophora. 



The Beroidcz further differ from Pleurobrachia in being 

 destitute of the long tentacular appendages so characteristic 

 of the latter, 



In Cestum^ or " Venus's Girdle," " elongation takes place to 

 an extraordinary extent, at right angles to the direction of the 

 digestive track, a flat, ribbon-shaped body, three or four feet 

 in length, being the result." 



DIVISIONS OF THE CTENOPHORA. The following arrange- 

 ment of the Ctenophora has been adopted by Gegenbaur (see 

 Greene) : 



Order CTENOPHORA. 

 Sub-order I. Stenostomata. 

 Family T. CALLYMMID^E. 



Body furnished with a pair of antero-posterior oral lobes, and other 

 smaller lateral appendages. Tentacles various, turned towards the 

 mouth. 

 Family II. CESTID^:. 



Body ribbon-shaped, extended in a lateral direction, without oral 

 lobes. Tentacles two in number, antero-posterior, turned towards the 

 mouth. 

 Family III. CALLIANIRID^E. 



Body produced into a pair of wing-like lateral lobes, bearing the 

 ctenophores. Tentacles two in number, lateral, turned from the 

 mouth. 

 Family IV. PLEUROBRACHIAD^E. 



Body oval or spheroidal, without oral lobes. Tentacles two in 

 number, lateral, turned from the mouth. 



Sub-order II. Eurystomata . 

 Family V. BEROID^:. 



Body oval, elongated, without oral lobes. Tentacles absent. 



