IV 



PHYLUM CCELENTERATA 



225 



stomach, and corresponding with them are eight bands of nemato- 

 cysts diverging from the apex of the ex-umbrella. If these 

 striking resemblances indicate true homologies, we must compare 

 the whole sub-umbrellar cavity of Ctenaria with the stomodseum 

 of Hormiphora, the margin of the bell of Ctenaria with the mouth 

 of Hormiphora, and the mouth of Ctenaria with the aperture 

 between the stomodseum and the infundibulum of Hormiphora. 

 But, as we have seen, the guUet of Ctenophora is a true stomo- 

 dseum developed as an in-pushing of the oral ectoderm, and has 

 therefore a totally different origin from the sub-umbrella of a 

 medusa. Moreover, the tentacles of Ctenaria have no muscular 

 base contained in the sheath, but spring from the margin of the 

 umbrella as in other Hydrozoa : its gonads are developed in the 

 rnanubrium, not 

 in the radial 

 canals, and there 

 is no trace of 

 an aboral sense- 

 organ. 



In the case 

 of Hydroclena, 

 found in Malay an 

 seas, the Cteno- 

 phoran resem- 

 blances, if only 

 superficial, are 

 much more strik- 

 ing. Hydroctena 

 (Fig. 175) is bell- 

 like, and provided 

 with a velum (7.). 



At its apex is an ampulla (ab.) bearing two lithites supported on 

 spring-like processes of the epithelium. From the apex of the 

 gastric cavity a canal is given off which extends to the sense-organ, 

 where it ends blindly, and from the sides a pair of short canals, 

 each of which terminates blindly at the base of the corresponding 

 tentacular sheath. Only two tentacles are present, with sheaths 

 at their bases : these are situated, not on the margin of the bell, 

 as in a medusae, but between it and the apex. There are no traces 

 of swimming-plates, and, so far as the evidence at present forth- 

 coming goes, there is not sufficient evidence to establish Cteno- 

 phoran affinities. 



On the other hand, the resemblance between transverse sections 

 of an embryo Ctenophore (Fig. 176, B) and of an embryo Actinian 

 (A) is very striking, and the presence of a well-developed stomo- 

 dseum, and of gonads developed in connection with the endoderm 

 and discharging their products through the mouth, may be taken 



VOL T. Q 



FIG. 175. Hydroctena salenskii. ab. aboral sense-organ ; 

 M. manubrium ; t. tentacle ; V. velum. (From the Cambridge 

 Natural History, after Dawydoff.) 



