978 HISTOLOGY AND NERVOUS SYSTEM OF CALCAREOUS SPONGES, 



I combine all these foi*ms with non-diffeventiated Eatoderm in 

 one Group, for which I adopt Polejaeffs term Homoccela, the meaning 

 of which word I adapt to the view explained aV>ove. 



All the other Calcai^eous Sponges possess a more highly differen- 

 tiated Entoderm. Ciliated chambers clothed with flagellate cells 

 are always present and the Oscular tube and adjacent canals are 

 clothed with pavement cells. I combine all these to form one 

 Group for which I likewise adopt Polejaeffs term, Heterocoela the 

 meaning of which word is likewise modified. 



MESODERM. 



The Mesoderm, which forms the bulk of the Sponge, consists of 

 Gallert of a pretty high degree of density. 



In this the Mesodermal cells are imbedded. In Calcispongise 

 the Gallert never shows a fibrillous structure as is the case in some 

 others Sponges. (Gumminse.) 



Also the Skeleton of these Sponges is produced by the Mesoderm. 

 The spicules always oi'iginate there and are always clothed with 

 Mesodermal cells or a Mesodermal cuticle, however far they may 

 protrude beyond its limits. 



THE TISSUE CELLS. 



In all calcareous Sponges numerous starshaped cells, with a 

 spherical nucleus, ai-e found in all parts of the Gallert, their proto- 

 plasmic processes are slender and vary in number from three to 

 ten. Generally they are simple, only exceptionally they may be 

 ramified. These cells are different in diff*erent Calcispongige in as 

 much as in some they are all alike with about five irregular pro- 

 cesses, whilst in others we find different kinds of these star-shaped 

 elements in the diff"erent parts of the body. The first is the case 

 in the Homocoela, the second in the Heteroccelia. Here we find 

 that in the central parts of the Mesoderm these cells have 

 numerous irregularly disposed processes, whilst they attain a 

 greater regularity towards the surface. The nearer they lie to 

 any free surface the more all their processes are influenced thereby 

 in such a manner that they run parallel to the surface in a more 



