Part 11. — Stichodactylince and Zoanthece. 153 



wall within the mesenterial spaces is sometimes much elevated. The number of 

 mesenteries is considerable, one small specimen possessed fourteen complete pairs, 

 and another eighteen. The mesoglcea is very thin, and the vertical retractor muscles 

 are extremely weak, so as to render it almost impossible to determine the directives. 

 I have been able to definitely ascertain the presence of the latter in onty one 

 instance, but others may occur. The parieto-basilar muscle, though weak, is 

 clearly distinguishable on each side. The endoderm is a thick, highly glandular 

 layer, and medium-sized stinging cysts are abundant in places. In some instances 

 the ccelenteron appears filled with the mucus extended from the endoderm cells. 



The mesenterial filaments consist only of the middle glandular streak or Nes- 

 seldrtisenstreif, the lateral ciliated streaks or Flimmerstreifen being absent (PI. xi., 

 fig. 4). They are seen to originate in direct continuity with the ectoderm of the 

 stomodeeum. At first, owing to the strongly folded condition of the stomodreal ecto- 

 derm the mesenterial filament is irregular, or rather the appearance is presented as if 

 a portion of the terminal region of the stoniodseum were still connected with the free 

 edge of each mesentery. It is only a little below the stomodseum that the ordinary 

 rounded appearance is assumed, but the Nesseldriisenstreif is never clearly marked 

 off from the mesenterial epithelium (PI. xi., fig. 4). The nematocysts in the upper 

 region are elongated and narrow, but below they are much larger, oval, and 

 strongly spinous. Different stages in the growth of the large tuberculated 

 nematocysts can be distinguished, the contents of the younger staining deeply 

 with cai'mine. The mature individuals present a peculiar appearance when a group 

 is cut through transversely. Irregular spine-like projections extend all the way 

 round the thick horn-coloured wall, the interior appeal's filled with some coagu- 

 lated substance, and here and there a cut end of the thread is indicated. The 

 spiral threads themselves are finely and regularly spirally marked. Towards the 

 free end of the mesenteries in the lower regions the endoderm is often loaded 

 with zooxanthellse. 



Of several specimens sectionized, only one contained reproductive organs, sper- 

 maria apparently in a dehiscing condition (PI. xn., fig. 3). The reproductive cells 

 are found in the interior of the mesoglcea, and in escaping break through the endo- 

 dermal tissue. They occur in only a few of the mesenteries. 



In three polyps dissected in the living condition, a few embryos were found. 

 They are large, dark-green, ovoid bodies, slightly narrower at one end, and 

 about 1 mm. in length. On cutting open the animal, they escaped freely into the 

 water. 



Prof. M c Murrich (1891, p. 303) found that the polyps retain the embryos in 

 the interior of the body until they are furnished with two or four perfect mesen- 

 teries. During the month of September I observed examples in process of partu- 

 rition. The disc and upper part of the column were almost entirely infolded, 



