3840 EDITH M. PRATT. 
due to a localisation of mesogloeal tissue alone (fig. 12), 
and in cross section have a rounded appearance. The 
thickenings vary in different species, in ‘““S. ehrenbergi” 
they are ‘05 mm. in diameter, in “8S. glaucum” ‘03 mm. 
They occur also in Xenia (Ashworth, 1898), but are much 
more feebly developed. They probably serve as additional 
supports to the autozooids when in an expanded condition. 
The musculature is typically Alcyonarian, but is much 
more strongly developed in the dimorphic Sarcophytum 
and Lobophytum than in Sclerophytum. In Alcyo- 
nium it is usually well marked, but is more strongly developed 
in the British species ‘A. digitatum” than in the tropical 
“A. pachyclados.” As in Alcyonium the retractor 
muscles are much larger than the protractors. The pleating 
of the mesogloea varies according to the development of the 
muscles. In Sarcophytum, Lobophytum, and Alcyo- 
nium the folds are numerous and very prominent, in 
Sclerophytum they are smaller and vary in size in 
different species. In the species “Scl. palmatum” and 
“Scl. capitale” they are not numerous, but are fairly 
large, but in the species “Scl. polydactylum” and “Sel. 
gardineri” the folds are very few and extremely small. 
The musculature of the mesenteries is more strongly developed 
in the upper than in the lower portions of the zooids. In 
the genus Sclerophytum it seldom extends below the 
terminal portion of the stomodzeum. ‘The musculature of the 
mesenteries of the siphonozooids is always feebly developed, 
as these individuals are only very slightly contractile. In 
the siphonozooids of Sclerophytum it is entirely absent. 
In the Alcyonaria the stomodzum is continuous with the 
mesenteries. Of the three layers which compose the stomo- 
deeum, only the endoderm and mesoglcea are continuous with 
the ventral mesenteries. There can be no doubt of the 
termination of the ectodermic epithelium of the stomodzeum 
at its aboral opening (fig. 8). Further reference is made to 
this fact (pp. 341 and 342). 
