Simpson — A Revision of the Oorgonellidae. 259 



V. — MyVCROsconc and Mi(;i!08copic Ciiahactkks as a Basis of 



ClASSlFICATION. 

 (1) COENENCHYMA. 



{n) Surface. — The surface of the coenenchyma is generally smooth to the 

 naked eye, but presents a glistening, arenaceous appearance when viewed 

 with a Ions. This is due to the small spicules, which project slightly, cither 

 singly or in small clusters. 



Thickness. — The tliickness varies in different species; e.g., in Jintcdla 

 juncca,^ Jtmcella gemmacea, and Scirpearia furcata it is usually thick ; but in 

 Jimcella racemosa, Scirpearia alba, and Scirpearia flagclhim it is generally 

 thin. 



On the other hand, however, extremes may be found in dillereut speci- 

 mens of the same species. No better example of this can be cited than 

 Jimicclla juncca (see later). For this reason the thickness of the coenen- 

 chyma cannot be regarded as a specific criterion. It does, however, affect 

 the general appearance of the colony, inasmuch as the verrucae are capable 

 of greater retraction in those specimens in which the coenenchyma is above 

 the average thickness. (See figs. 9 and 10 («, h, and c) of Juncella juncea> 

 fig. 100 of Scir2Karia andaiiiancnsis, and figs. 83 and 88 of Scirpearia furcata.) 

 As a contrast to these, figs. 49 and 56 of Scirpeccria flcujcUum may be taken 

 as typical. One very important feature in regard to the thickness of the 

 coenenchyma is the fact that this is almost a constant in any one specimen ; 

 the difference in the thickness of the colony is really due to the axis. 



It, therefore, follows that, although the thickness of the coenenchyma 

 varies very little in any individual specimen, it may vary considerably in 

 different specimens of the same species, and is therefore of little if any 

 taxonomic value. 



Consistency. — The coenenchyma is densely packed with minute spicules, 

 and is consequently very granular and brittle, especially when dry. It 

 presents a gritty, uneven surface when cut with a l^nife. 



(h) Histology. — The coenenchyma is divided into an outer non-canal- 

 bearing part in which the polyps are embedded, and an inner part in which 

 small canals ramify in all directions (figs. 10 and 19). These are separated 

 by a series of longitudinal canals, which are arranged peripherally. The 

 proportionate thickness of these two parts varies greatly in different 

 specimens, and is of no taxonomic value. 



' The generic and specific names given in this part of the memoir are those which are adopted in 

 the final classification (cj.v.). 



