THE ANATOMY OF ALOYONIUM DIGITATUM. 369 



I have searched iu vain for anything corresponding to the muscular fibres 

 of Vogt and Yung's account, and I am quite convinced that neither in Al- 

 cyonium digitatum nor in A. palmatum are there any muscular fibres iu 

 the mesogloea. It is quite possible that some of the cells lying in the meso- 

 glcea may be to a certain extent contractile, but they are quite different in 

 appearance from the muscular processes of the endoderra-cells lining the coelen- 

 tera, which will be described later on. 



The chemical characters of the homogeneous substance which 

 forms the bulk of the mesogloea are described in a paper by 

 Brown, which appears in this number of this Journal. 



Spicules. — The spicules of Alcyonium digitatum 

 present so many varieties of form, that it is not possible, without 

 writing a long treatise on this subject, to do more than give a 

 description of a few examples. 



The general impression obtained by examining a slide of 

 spicules, made by boiling a small branch of Alcyonium 

 digitatum in potash, is that no two spicules in the field ot 

 the microscope are alike. 



The majority, however, are somewhat like a dumb-bell in 

 shape (fig. 3, a, b, c), with numerous irregular and blunt 

 projections at each end, and about O'l mm. in length. In 

 addition to these there is a considerable number of larger 

 (0*2 — 0'3) spicules, which are branched {d) or shaped like a 

 capital K, or simply crosses with numerous blunt projections. 

 A few spicules may be seen scattered about among the more 

 characteristic forms which are quite irregular in shape, some 

 with a central plate-like centre from which spring a few short 

 branches (fig. 3,/), some with two or three long arms and 

 one or two short ones, some very small ones like spheres 

 covered with irregular tuberosities, and others of many 

 different shapes and sizes. 



In all preparations such as the one mentioned, in which the 

 tentacles, the disc, &c., of the polyps are boiled down with 

 the other part of the colony, there may be seen a certain 

 number of long unbranched lancet-shaped spicules (fig. 42, e) 

 covered with irregular tuberosities. They vary very much in 

 shape, some being like a thick pin (without its head), others 



