ANATOMY OF MTJSSA AND EUPHTLL1A. 31 



secondly, because it shows that this enormously and peculiarly 

 developed stomodseum is digestive in function, which might, 

 indeed, have been inferred from its extent, and from the almost 

 complete absence of a ccelenteron as a cavity. 



The mesogloea is a thin but perfectly distinct, structureless 

 lamina, everywhere separating the ectoderm from the endo- 

 derm. The endoderm cells lining the extrathecal parts of the 

 ccelenteron are vacuolated, and do not fill up the cavities, but 

 in the intrathecal parts of the polyp the endoderm cells are 

 entirely converted into a parenchymatous tissue, filling up all 

 such parts of the ccelenteron as are not occupied by mesenterial 

 filaments. My specimens were not sufficiently well preserved 

 to admit of my giving an account of the histology of this 

 tissue. It is filled with nematocysts, one of which is repre- 

 sented in fig. 12, and may be seen to be of an entirely different 

 character to those found in the ectoderm, being of smaller size 

 and different shape. The axial tube is distinguishable, and the 

 thread coiled in an oblique spiral within the capsule* I could 

 not find any of these nematocysts with the thread ejected. 

 Numerous zooxanthellse also exist within the meshes of this 

 tissue. 



The muscles on the mesenteries are well developed, and 

 exhibit the relations of the exocceles and entocceles. The septa 

 are all entoccelic. 



Ova are borne on the tertiary mesenteries and on them only. 

 The ovaries are of large size and bulge out the mesenteries to 

 such an extent that they nearly fill up the exocceles and ento- 

 cceles in that region. They are always developed towards the 

 peripheral ends of the mesenteries. Each ovum is surrounded 

 by a number of large granular masses the granules of which 

 stain very deeply in borax carmine. At first I mistook these 

 for testes, but from their relation to the ova and their 

 resemblance to nutritive cells in Pennaria Cavolinii and 

 Tubularia mesembryanthemum, I have no doubt that 

 they are nutritive cells destined to be absorbed by the ovum 

 (vide fig. 8, ov.). That one out of several primitive ova should 

 develop into a mature ovum at the expense of the others has 



