118 THE BERMUDA ISLANDS. 



ternal to the tentacles, so as to form a deep fosse around the 

 peristome (PL 11, fig. 1), which, however, does not rise above 

 the level of the margin. I was not able to distinguish in any 

 of my preparations the delicate mesogloeal processes of the disc 

 which support the ectodermal muscle cells in D. delicotula, but 

 it is possible that they had been macerated away. 



The mesogloea of the stomatodseum is raised upon its ecto- 

 dermal surface into prominent but rather delicate ridges, over 

 which the ectoderm is folded. The gonidial grooves are deep, 

 and as in Ouladis are prolonged below the level of the internal 

 opening of the stomatodaeum, and have the mesogloea thick- 

 ened. In D. delicatula Hertwig describes the gonidial grooves 

 as being hardly marked in the stomatodseum, and if this is 

 found to be an invariable characteristic, it will be necessary to 

 alter slightly the definition of the Phyllactida3 given above. 

 The depth of the grooves, and their prolongation downwards, 

 are so marked in the other members of the group that I have 

 examined, as to suggest that the apparent shallowness in the 

 specimen examined by Hertwig may be due to distortion. 



The primary and secondary mesenteries are perfect through- 

 out the whole length of the stomatodseum ; the tertiaries are 

 perfect in their upper part, but lower down separate from the 

 stomatodacum ; while the fourth cycle consists entirely of im- 

 perfect mesenteries. The directives are attached throughout 

 a greater part of their length than are any of the other mesen- 

 teries, owing to the prolongation of the gonidial grooves. The 

 longitudinal muscles in the upper portion of the mesenteries 

 form a low band, covering the greater portion of thenon-gono- 

 phoric region of the mesentery ; internally the muscle processes 

 end rather abruptly, but externally they gradually diminish 

 in size. In the lower part of the mesentery, below the level of 

 the stomatodacum, the arrangement of the muscle processes is 

 very different (PL 10, fig. 6). Throughout the greater portion 

 of the non-gonophoric region of the mesentery they are very 

 small, but as the gonophoric region is approached they sud- 

 denly increase in size, forming a strong projection, and then 



