OF THE MOLLUSCOIDA AND CCELENTERATA. 517 



The property of gemmation in a marked manner distinguishes the Mollus- 

 coicla from the MoUusca proper, on the one hand, while it associates them quite 

 as obviously with the Coelenterata on the other. We know nothing of a process 

 of this kind as occurring in the so-called Ctenophora, including the families Cal- 

 lianiridce* and Beroidce ; but the organisation of these animals, first rightly con- 

 sidered by Frey and Leukart abroad, and by Professor Huxley at home, referred 

 them to the higher section of Coelenterata, namely, the Actinozoa. Yet, the more 

 I have studied Cydiijpe, the more it has appeared to me to hold a position be- 

 tween the Actinozoa and the Polyzoa, linking the two by characters which it 

 exhibits in common with either, or both. Indeed, in any other place it would 

 seem to be not only friendless but intrusive. A view similar to this has, I believe, 

 been already expressed by M. Vogt, but I regret that T have not access to his 

 observations on the subject. 



It is curious to observe the progressive development of the digestive system, 

 proceeding from the Hydrozoon onwards through the Actinozoa, Ctenophora, and 

 Polyzoa, to the Tunicata. 



The important part taken by the Ctenopliora as a link in this beautiful chain, 

 is represented in the accompanying series of diagrams. Moreover, certain points 

 in the structure of these animals, are even made more tangible to our philosophy 

 by the light which is thus shed upon them. 



The stomach of Cydippe is connected with the walls of the body by two 

 vertical septa, with two interseptal loculi. The coecal tubes forming the lining of 

 these loculi run forwards as far as the mouth, and are at once diverticula of an 

 alimentary system and of a somatic cavity. 



We observe here, as in Actinia, a well defined internal gastric opening, bounded 

 by two crescentic folds, determined by the persistence of the before-mentioned 

 loculi. These latter communicate below with the rudimentary intestine which is 

 yet little more than a central tubular narrowing of the somatic cavity, from the 

 gastric end of which also pass off the two dichotomously-branched tubes, which 

 terminate peripherily in the fusiform sinuses,f corresponding with the ciliated 

 bands. All this afibrds us a more distinct idea of the mode in which the intes- 

 tinal tube is formed. Thus, instead of arising simply as an extension of the 

 proximal end of the stomach, the whole gut is at first but a tubular process of 

 endoderm, inclosing a portion of the somatic cavity. In Cydippe, the intestine 

 is perfectly straight and axial, reaching the posterior extremity of the globose 

 body, where it exhibits a small, but distinctly marked bifurcation, and the little 

 nervous ganglion, with its otoconical sac, is received into the intervening recess. 



* This family name is objectionable, as having been chosen from a supposititious genus founded 

 , upon a mutilated specimen of Cydippe, indifferently drawn. 



f Would it be too far-fetched to suppose that these sinuses are, as it were, retrospective of the 

 tentacula of Actinia 1 



