PROFESSOR ALLMAN ON THE RELATIONS OF THE CCELENTERATA. 



465 



Leuckart insisted on the association of the Ctenophora with the Actino- 

 zoa rather than with the Hydrozoa, and the same view of their affinities has 

 been advocated by Huxley. According to this conception of ctenophoral 

 homologies, the ctenophore must be provided with a stomach-sac, differentiated, 

 as in the actinozoon, from the general body cavity. Now, though the somatic 

 cavity in Beroe suddenly diminishes towards the aboral end, and is there pro- 

 vided with a pair of valve-like folds (fig. 12, s), so that the entire tract admits 

 of being distinguished into two regions, it is nevertheless as continuous and 

 simple as in Hydra. 



The advocates of the actinozoal nature of the Ctenophora see in the canal 

 system of a Beroe or a Cydippe the radiating chambers of an Actinia, separated 

 from one another by partitions of relatively enormous thickness. I do not 

 desire to dispute the correctness of this view. We have already compared a 



Fig. 13. 



Fig. 12. — Diagramatic longitudinal section of Beroe in a plane at right angles to that of the compressed somatic cavity. 

 In order to give a sufficiently comprehensive view of the structure, a few parts are here represented, which are in reality 

 somewhat removed from the plane of the section, a, a, Transverse portion of the radiating canal system, two of the 

 primary liranch.es being shown as if cut off close to their origin ; x, x, meridional portion of this system ; x' x 1 , deep or 

 accessory canals, their distal ends cut off ; b' V, somatic cavity ; c, lumen of circular canal ; t, one of the aboral outlets 

 of the somatic cavity ; V V, somatic cavity ; t, external opening of one of the aboral canals ; s, valve-like processes of 

 the inner surface of the somatic cavity ; d, d', generative sacs, male and female. 



Fig. 13. — Diagramatic transverse section of Beroe,. b', Somatic cavity ; x, x, meridional portion of the radiating 

 canal system ; x', x', deep or accessory canals ; d, d', generative sacs, male and female ; y, vibratile lamellae. 



hydroid with an actinozoon, and have seen in the radiating canals of a hydroid 

 medusa the homologues of the radiating chambers of an actinia ; so that, even 

 though the Ctenophora be truly Hydrozoa, we must expect to find in them the 

 same points of agreement with the Actinozoa which we have endeavoured to 

 demonstrate for the other hydrozoal orders. 



Now, the fact of the radiating canals being widely separated from the axial 

 cavity instead of being adnate to it, is exactly the point which essentially dis- 

 tinguishes a hydrozoon from an actinozoon ; and the fact of the intervening 

 space being in the ctenophore obliterated by the interposition of a voluminous 

 gelatiniform mass does not alter this relation, for it is exactly what we find in 



