112 Natural History Bulletin. 



throughout the region lying between this axis and the surface. 

 In some places they are met with in such profusion as to sug- 

 gest real plexuses. They connect with the primary canals, 

 wind in a tortuous course among and around the spicules, 

 anastomose freely, and serve the purpose of true capillaries in 

 facilitating the contact of the water-vascular fluid with the 

 living, active cells of the zoanthodeme. The secondary 

 canals are probably without cilia, the water being forced 

 through them by the constant action of the ciliated endothelial 

 cells of the primary canals. 



Histologically, these canals present good reasons for con- 

 sidering them homologically capillaries. The figures of capil- 

 laries in Gray's Anatomy on page 83, would answer fairly for 

 a representation of the secondary water-vascular canals. The 

 same delicate, transparent tube that is seen in the figure will 

 be found in the coral, and similar nuclei scattered over the 

 surface of the tube. The nuclei, however, are larger and 

 more numerous in the coral than represented in the figure. It 

 is interesting, moreover, to note that these two structures — 

 the secondary water-vascular canals, and the capillaries of the 

 higher animals — are both mesodermal in origin, a fact that still 

 further strengthens the evidence in favor of real homology. 



In concluding the description of this species, it may be 

 instructive to give a tabulated statement of the origin of the 

 various parts described. 



Ectodermal — The epithelial investment of the zoanthodeme 

 and of the individual polyps; the lining of the 

 gullet. 

 Mesodermal — The "basal substance" forming the middle plate 

 of each mesentery; the portion of the gullet be- 

 tween the investing endoderm and the fining 

 ectoderm; that portion of the body wall and ten- 

 tacles of each polyp which is found immedi- 

 ately beneath the ectoderm; the "matrix" of 

 the zoanthodeme; and the wall of each calicle 

 beneath the endoderm; the spicules; stellate 



