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Show 566 DR. R. VON LENDENFELD ON THE SYSTEMATIC [Dec. 21, a special Subkingdom for the Sponges. They are evidently Metazoa, and no doubt Coelentera in the sense given above, namely the Grade Coelentera as opposed to the Grade Ccelomata. I think therefore that the Sponges form part of the Grade Coelentera, and I do not believe that any one will raise any objection to this statement. Now, however, we have to approach a much more difficult task, and that is, to ascertain what position the Sponges occupy within the Grade Coelentera. In this Grade we must place, besides tbe Sponges, one very well-defined group of animals (the Jellyfish, Hydroids, Corals, and Cteno-phora) which is not connected with other animals by any intermediate form. There can be no doubt of the comparatively close affinity of all these, and the sharp distinction between them and the Sponges. In a like manner the Sponges are an exceedingly well circumscribed group, without any transitions in any direction to other animals. The Grade Coelentera comprises, therefore, two well-defined groups:-(1) the Mesodermalia(910) or Sponges ; and (2) the Epithelaria (910) or Nematopbora (Lankester), Cnidaria (Claus), Telifera (Marshall), as they are variously termed. A. In the Mesodermalia the arcbenteron communicates with the outer water by numerous small pores through which the water-current enters; and by one or a few larger pores termed oscula or vents, through which the water is expelled. It consists here of a branching canal-system. In the Epithelaria there is no branching canal-system. The anus and mouth are not distinguished, and the mouth or mouths are equivalent to all the openings of the canal-system of sponges. Only exceptionally two different kinds of pores are met with, as in certain Actiniae with terminally open tentacles; but there is no regular current of water through tbese pores. B. The gastrula of the Mesodermalia is generally produced by invagination. The gastrula of the Epithelaria, on the other hand, is generally the result of delamination. C. The Mesodermalia have no movable appendages wherewith to catch their prey. The Epithelaria have such appendages. D. The Mesodermalia are not armed with cnidoblasts or their homologues. The Epithelaria are defended by cnidoblasts or their homologues. Although these differences are important, yet the principal distinction between these two groups, to which I drew attention at the last meeting of the British Association (Meeting 1886), is the following :- E. The Mesodermalia have invariably simple ectodermal and entodermal epithelia, the cells of which are always flat pavement-cells, and never converted into muscular, glandular, sexual, or sensitive elements. The muscular, connective, slime-producing glandular, skeleton-producing glandular, sexual, sensitive, ganglionic and amcei |
