344 



THE INFLUENCE OF LIVING SURROUNDINGS. 



work, with the meshes and branches spreading almost in a 

 plane ; snch forms are tolerably common among the true 

 sponges. Besides this, all the branches have large perforations 

 on one side, which in living examples if I may judge from the 

 points of attachment appear all to be directed upwards. If 

 such a branch is cut across, certain peculiar thick transparent 



FIG. 93. Spongia wftiligmea, Esper. Sections of branches showing the skeleton formed 

 by the filaments of the sea-\veed and the stomata, a, of the sponge. The spiculas and 

 protoplasmic tissue are cnly visible under a high magnifying power. 



fibres appear which do not greatly resemble the usual fibres of 

 sponges, and which penetrate the whole organism in every direc- 

 tion and through all its anastomoses. Still, when we again 

 study the uninjured organism, even with a lens, we feel once 

 more inclined to agree with Espsr in regarding it as a true 

 sponge. 



But a more minute investigation with the microscope shows 



