THE ANATOMY OP ALOTONIUM DIGITATUM. 367 



cells, '' arranged so as to form a long solid band on the edge of 

 the septum (i. e. mesentery). As seen in sections this band 

 has a bilobed form, or, in other words, a longitudinal groove 

 runs along its middle" (fig. 18). I have never seen the Y-shaped 

 appearance of this groove in section which Wilson describes in 

 Fuuiculina, but in several sections I have seen the lobes folded 

 over so as to form an almost complete canal (fig. 16). 



The cells of the groove are in appearance and in detail 

 similar to those of the stomodseum. 



As regards the ventral mesenterial filaments my observations 

 do not coincide in all respects with Wilson's figures and descrip- 

 tion of these filaments in Paralcyonium. Like Wilson, I recog- 

 nise that there are essential and very important difi'erences 

 between these filaments and the dorsal ones. There is no 

 median groove, there is no sharp line of demarcation between 

 the cells of the filament and the neighbouring endoderm-cells 

 of the mesenterial epithelium, and the cells are not all of the 

 same kind, some staining very much more deeply than others 

 (fig. 19). Two distinct kinds of cells may be made out in good 

 preparations with a high power : first, large non-ciliated gland- 

 cells, which stain deeply with heematoxylin ; and second, 

 elongated columnar cells filled with numerous minute granules. 



The mesogloea of Alcyonium is composed of a thick homo- 

 geneous substance containing (1) endodermic canals ; (2) solid 

 cords of endoderm ; (3) minute isolated cells connected with 

 one another and with the endoderm by fine anastomosing fibrils; 

 (4) spicules of calcium carbonate. 



(1) The endoderm canals — that is to say, cords of endo- 

 derm containing a lumen which communicates with the 

 coelenteron of one or more of the polyps — are chiefly found in 

 the superficial parts of the colony. They consist of a single 

 layer of endoderm-cells embracing a narrow lumen, which 

 becomes obliterated in some of the branches (figs. 13, 17). 

 The canals then are continuous with — 



(2) The solid cords of endoderm which are found 

 throughout the mesogloea of the colony, and may be easily 

 studied by osmic acid or methyl blue preparations of fresh sec- 



