E. MARSHALLI. — GEN. ARRANGEMENT OF SOFT PARTS. 123 



more words of comment. Noteworthy is the fact that in that 

 species the dermal membrane is scarcely sufficiently developed to 

 deserve being called membranous. In other words, the limiting 

 trabeculœ of the external surface are generally as thin and 

 cobweb-like as, and in no way distinguishable from, those of 

 the deeper parts. The meshes of the surface, or the ' pores,' 

 bounded by such trabeculœ are exceedingly various and irregular 

 in shape and size, just like any intertrabecular lacunœ seen on 

 sections of the sponge-wall. However, occasionally in the spaces 

 between the conuli the limiting trabecular are found flattened out 

 into the form of a narrow band or of a nodal expansion (PI. 

 IV, fig. 23), which, so far as it extends, gives a more or less 

 rounded outline to the meshes bounded by it. In E. aspergillum, 

 as described and figured by F. E. Schulze, the dermal membrane 

 should be well developed as such ; so I have found it likewise 

 in E. imperialis, or, at any rate, more extensively membranously 

 formed than in E. marshalli. On account of the cobweb-like 

 nature of the entire ectosomal trabeculai in the last mentioned 

 species, the conuli, when seen from the sides, appear more like 

 the rigging of a schooner's mast (PI. V, fig. 36) than like conical 

 tents, which they would certainly resemble if only a continuously 

 developed dermal membrane were present.'-' 



* W. Marshall ('75, fig. 62) has described and figured the dermal membrane of a 

 young E. aspergillum as regularly possessing a single, rather small pore to each quadrate 

 mesh of the dermal latticework. This has been shown by F. E. Schulze ('80, p- 666) not 

 to hold true in old specimens, in which the pores had been found to be more numerous and 

 crowded so as to leave less space between them. However, Schulze declared himself 

 willing to believe that in the young the pores might be distributed in the manner described 

 by Marshall. In quite young specimens of E. imperialis as well as of E. marshalli, I find 

 not only the dermal membrane but also the gastral and the canalar membrane respresented 

 by quite thin trabecuke, which are nowhere membranously developed. I regard this as the 

 primitive condition of the trabeculœ at the surfaces and the membranous state as being 

 acquired after a certain stage of growth. 



