196 J. E. DuERDEN — Jamaican Actiniaria : 



the oval nuclei of wliich are arranged at different heights in the different cells, so 

 that a distinct, deeply-staining, nuclear zone is produced in sections (PI. xv., fig. 4). 



In transverse sections, a little above the stomodseal termination, the reflected 

 ectoderm is thrown into a few short vertical folds, and centrifugally is free from 

 the mesentery, while centripetally it can be traced in continuity with the ectoderm 

 of the stomodfeum. 



This continuity is, however, not one of exactly similar tissues throughout, but 

 is interrupted at places by a tissue of a different nature. The cell nuclei of this 

 are rounded, and not arranged in a distinct zone, and the whole stains less deeply 

 and contains zooxanthellse and granular gland cells. To this tissue, as met with 

 in Zoanthus cMerchice, von Heider (1895, p. 129) has applied the term Drtisen- 

 wulst." Though its presence can be easily recognized in P. tnnicans, it is not so 

 well developed as in the genus Zoanthus, where, owing to the increased size and 

 length of the polyps, the reflected ectoderm and mesenterial filaments are better 

 displayed and more favourable for study. 



As shown in PI. xv., fig. 4, a filament is a complex structure, the sagittate or 

 lanceolate form in transverse sections being characteristic of the Zoanthese. The 

 outer border of the lateral lobes is constituted of ciliated, extremely narrow 

 cells, the associated nuclei forming a very regular, densely-staining zone. It 

 is to this tissue that I consider the term ciliated streak or Flimmerstreif should 

 be restricted, and not applied to the lateral lobe as a whole, as is usually done. 

 The inner layer of the lobes is formed of endoderm cells, indistinguishable from 

 the epithelium of the mesentery. The tissue occurring around the termination 

 of the middle lobe is made up of ciliated supporting cells, granular gland cells, 

 and nematocysts. The term glandular streak, Driisenstreif, or Nesseldrtisenstreif 

 should, in my opinion, be employed only for this part of the middle lobe, the 

 intermediate streak coming between it and the ciliated streak. Towards its 

 termination the mesogloea is slightly swollen, and delicate muscular fibres border 

 it anteriorly. 



The mesenteries exhibit the macrocnemic arrangement, that is, the dorsal, 

 or sulcular pair of imperfect directives has a pair of mesenteries on each side — 

 of which the first is a perfect mesentery, and the other an imperfect — and the 

 succeeding pair consists of two perfect mesenteries (PI. xv., fig. 4). Beyond these 

 the pairs consist of an imperfect and a perfect mesentery until the neighbourhood 

 of the ventral or sulcar directives is reached, when the arrangement in pairs 

 becomes a little irregular, this being the region in which new mesenteries are 

 added. In one polyp eight perfect mesenteries occurred on each side, while 

 in another eight were present on the left and six on the right side. 



The mesenterial musculature is extremely feeble, and the parieto-basilar is 

 clearly distinguishable. The mesogloea is broad at its origin in the column-wall, 



