THE HISTOLOGY AND NERVOUS SYSTEM OF THE 

 CALCAREOUS SPONGES. 



By R. von Lendenfeld, Ph.D. 



Like other Sponges, the Calcispongiee consist of Entoderm, 

 Mesoderm and Ectoderm. Tlie Mesoderm is the only layer which 

 is highly diflerentiated. Ectoderm and Entoderm are formed by a 

 single layer of cells. The outer surface of the Sponge doubtlessly 

 is Ectodermal and the cells which line the Oscular tube, the ciliated 

 chambers and the excretary canal system can with equal certainty 

 be determined as Entodermal. The Epithelium of the introductory 

 Canals is in all probability in the greater part Ectodermal, in a 

 small portion Entodermal. 



ENTODERM. 



The Entoderm is veiy simple, but nevertheless shows a higher 

 development than the Ectoderm, In some Calcareous Sponges it 

 consists of one kind of cells only ; the oxxlinary flagellate elements 

 with frills. In others again only part of the Entodermal Epithelium 

 is composed of such cells, whilst another part consists of simple, low 

 pavement cells. Where such a differentiation occurs, the flagellate 

 fringe-cells are found in the outer and middle part of the body, 

 lining the ciliated chambers or their homologa, whilst the pavement 

 cells clothe the Oscular tube and the exhalent canals leading from 

 the ciliated chambers to the Oscular tube. 



Those Sponges, which Haeckel comprises in his Family Ascones, 

 Leucosolenia Bowerbank, which possess a simple tube shaped 

 gastral cavity and in which no ciliated chambers are developed, 

 possess flagellate Entodermal cells only. The same is the case with 

 an Australian Sponge which possesses ciliated chambers like the 

 Syconidae, recently described in these Proceedings. 



