BY R. VON LENDENFELD, PH.D. 319 



"Whether numerous invaginations as those which according to 

 F. E. Schulze form these canals, ought to be compared to the 

 invagination of the Gastrula, it is here not the place to discuss, 

 but if we followed this custom throughout, we would have to call 

 the sweat glands in our skin also Entodermal, because they are 

 produced by an invagination of the Ectoderm. 



I think that an invagination of Ectoderm can never produce an 

 Entoderm, but that an Entoderm can only be produced from an 

 indifferent Blastula which does not consist of Ectoderm. In the 

 case of the Sponge Embryo the outer surface is covered by Ecto- 

 derm, and the invaginations take place after the Entoderm has 

 been formed. 



The statement of Marshall, that the canals taking their origin 

 between the Entodermal ciliated chamber, and the Ectodermal 

 surface layer, by these two layers moving away from each other, 

 after they have grown together (Plakina), may be formed as likely 

 from the ciliated chambers as from the Ectodermal surface, appears 

 indisputable ; and I gladly accept it, because the digestive func- 

 tions which I ascribe to the Epithel of these canals and the sub- 

 dermal cavity, perhaps also point to an Entodermal origin of 



those cells. 



2. Entoderm. 



Whilst the Ectodermal cells, although performing manifold 

 duties, are apparently (only few Sponges have been investigated 

 with sufficient care) of a uniform shape, the Entodermal Epithelia 

 are different in the different parts of the Sponge. In the ciliated 

 chambers they are elongate, cylindrical, and contain a Protoplasma 

 which imbibes colors very freely ; in the canals leading from the 

 chambers to the oscular tube, and on the surface of the latter they 

 resemble the Ectodermal cover cells, although they never appear 

 quite so low as these (Aplysillidse, von Lendenfeld). The ciliated 

 chambers in the Calcispongise often have the shape of long tubes 

 (Radial tubes Syconid?e). In all other Sponges they are pear- 

 shaped, sometimes elongated and sometimes nearly spherical 

 They vary very much in size. (Sack-Birn-Halb.-Kugel fbrniig, 

 F. E. Schulze). 



