646 RECORD OF CURRENT RESEARCHES RELATING TO 



organs of the Cliarabydoicla, Discopliora, and Calycozoa ; into these 

 details we cannot enter, but we give a brief resume of their general 

 conclusions. Putting aside the very distinct group of sponges, it is 

 possible to divide the rest of the Ccelenterata into two great gi'oups ; 

 (1) Ectocarpa, (2) Entocarpa ; ia the latter are all the Anthozoa and 

 Acraspedota (with also the Charabydeida and Lucernarida), and in the 

 other the Hydromedusse (including the Siphonophora) and the Cteno- 

 phora. The most important difference between these two groups lies 

 in the fact that in the former the generative organs are derived from 

 the ectoderm, and in the latter from the endoderm ; in one, therefore, 

 the organs are exposed, and in the latter they are placed in j)rocesses of 

 the gastro-vascular system. Other minor differences remain to be noted ; 

 in all the Entocarpa the matured generative products lie separately in 

 the mesoderm ; in the Anthozoa they are invested by fibrous connective 

 tissue, and in the Acraspeda by gelatinous capsules. This is not the 

 case with the Ectocarpa. Nor, again, is the mode of emission similar 

 in the two divisions ; in the Entocarpa the products pass into the gastro- 

 vascular system, while in the Ectocarpa, with the possible exception 

 of the Ctenophora, they pass directly into the water. The two 

 groups may be thus conveniently and succinctly defined : — 



The Entocarpa are Ccelenterata, in which the generative cells are 

 developed in the endoderm, and pass when mature into the mesoderm ; 

 they are provided with a special secreting apparatus (the mesenterial 

 filaments). 



The Ectocarpa are Ccelenterata, in which the generative cells are 

 developed in the ectoderm, where they remain ; they do not possess 

 any mesenterial filaments. 



Other differences may be noted between these groups, but passing 

 to their common origin, it may be noted that the original ancestor 

 was doubtless very similar to Hydra, though somewhat more gene- 

 ralized in character, and with a much less marked differentiation 

 of ectoderm and endoderm. The generative products had no defined 

 seat of origin ; when this began to obtain two distinct phyla were 

 initiated ; one led by the Hydroid Polyps to the Ctenophora, the 

 other to the Scyphistoma-creatures, in which the generative organs had 

 an endodermal origin, and in which the gastric cavity was interrupted 

 by four longitudinal septa ; this division broke up into the Anthozoa 

 and the Acraspeda. 



Some few points as to the histological details of the AdinicB 

 remain to be summed up : — 



(1) The organs are chiefly developed from the ectoderm. 



(2) There is a striking similarity between the histological elements 

 of the ectoderm and endoderm. 



(3) The neuro-muscular system is made up of three sets of cells, 

 muscular, sensory, and ganglionic, and these are connected into one 

 system by nerve-fibrils. 



(4) The muscular fibres seem to have been primitively arranged 

 in lamellfe. They grew inwards, and became separated into bundles 

 by the investing connective tissue. 



(5) Where no special optic organb arc developed, some, at any 



