THE ANATOMY OF THE MADREPORARIA. 
587 
specimens had any trace of such, and from observations on 
Desmophvllum, a closely allied form, I imagine that these 
tissues were simply due to the expansion of the polyp, and 
contained a continuation of the ccelenteron such as was 
described by v. Heider in Cladocora. On decalcification the 
polyp appears conical, and divided into a series of wedges by 
the spaces where the septa had been. At the base of the 
polyp, i.e. the apex of the cone, these wedges appear to be 
connected together by little bridges of tissue; these latter are 
of no morphological importance, being due apparently merely 
to the incompleteness of the columella, and their arrangement 
varies in different specimens. The polyp consists of a mouth- 
disc, bearing tentacles : a stomodseum, which opens into the 
ccelenteron, the latter being periaxially divided into exocoeles 
and entocoeles by the mesenteries. 
The mouth-disc (fig. 2, md) is peripherally fastened to 
the extreme edge of the lip of the calyx, and is centrally 
invaginated into the typical Anthozoan stomodseum. 
On the disc are borne the tentacles, which are simple 
hollow evaginations of the entocoeles, i.e. one is placed over 
each septum. They are covered by small prominences, each 
of which is a “ battery ” of nematocysts. I have not been able 
to determine whether they possess an opening at the tip or not. 
They vary in size and position according to the order to which 
they belong, the primary tentacles being the largest and the 
nearest to the mouth. ( Vide Moseley ( 11 ), pi. xvi, fig. 12.) 
The mouth is oval in outline, and at each end of its long 
axis is in most cases a well-marked gonidial groove. 
Through the periphery of the mouth-disc protrude the 
acontia. I have by a fortunate section been able to satisfy 
myself that they are ejected through definite openings, not by 
rupture of the disc ; these are therefore directly comparable to 
the cinclides of Actiniae. 
A mesentery of the first order is drawn in fig. 5 to show 
the general trend of the muscles, though they are much more 
numerous than there represented. They are best seen by 
mounting the mesentery whole in glycerine. 
