156 Natural History Bulletin. 



studied. It is worth while to note, however, that the largest 

 spicules are found in the species having exserted calicles. 

 Perhaps a general rule might be stated as follows: 



The largest spicules are found in species having exserted 

 calicles, and the smallest spicules are found in the species hav- 

 ing included calicles and a thin coenenchyma. 



Basal substance . The cosnenchyma is so full of spicules and 

 cells that there is very little of the basal substance to be seen, 

 The mesodermal cells seem to be oval or quadrate in form, 

 few, if an}^, t3'pical "stellate mesodermal cells" being visible in 

 my sections of this species. 



Water-vascular systeim. The Primary canals are not 

 well differentiated from the secondar3\ On account of homo- 

 logical considerations, however, I shall consider those canals 

 which immediately surround the axis as primary canals. 

 These vary greatly in size and section (PI. X, fig. 5), and 

 also in number, which, however, is less than in previous 

 species. The calicles often open directly into primary canals 

 as in Mnricea. The endothelial lining of both primary and 

 secondary- canals seems to be unusually thick as if composed 

 of several layers of cells. 



The Secondary Watcr-z-ascular canals are not particularly 

 numerous. They often serve to connect calicles with the 

 primary canals, and sometimes go directly from one primary 

 canal to another (tigs. 5 and 6, PI. X). There is less regu- 

 larity in the arrangement and distribution of both classes in 

 this than in the other species studied. 



The Capillaries are exceedingly numerous and are almost 

 equally distributed throughout the coenenchyma. There 

 seems to be a correspondence between the size of spicules and 

 the relative number of secondary canals and capillaries. 

 Species having large spicules have very numerous secondary 

 canals and comparatively few capillaries; while those having 

 small spicules have few secondary canals and many capillaries. 

 This doubtless is brought about mechanically. Large spic- 

 ules have large spaces between tiiem and consequently there 



