Two Peculiar Actinian Larvce from Tortugas, Florida. 



'S3 



are plainly zooxanthellas, and between the nuclei of the ciliated cells and 

 the mesogloea is a finely granular or fibrillar layer, which resembles the 

 fibrillar layer at the base of the ordinary epithelium. The boundary be- 

 tween the ciliated plate and the ordinary ectoderm is sharp and distinct and 

 there are apparently no transitional cells between the two. The ordinary 

 epithelium does not overgrow the ciliated band at its margins as in the case 

 of Zoanthella galapagoensis. In the latter species the ciliated cells are much 

 longer, as compared with the ordinary ectoderm, than in the Tortugas species. 



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Fig. 3. — Section through ciliated band and adjoining ectoderm of 

 Zoanthella. Flagellated cells extremely long and slender, 

 appearing like masses of spermatozoa; among them a few 

 larger cells, and at hase of epithelium is a granular zone. 

 Mesoglcea is very thin beneath ciliated plate, but at edges 

 very thick. X 333. 



In Zoantliina the ciliated band is circular and of nearly uniform width ; 

 in Zoanthella it is longitudinal and varies much in width, being widest in 

 the middle and narrower at either end. In some specimens of Zoanthella 

 the band is apparently double, being divided along its middle by a line of 

 clear, non-ciliated cells (figs. 13-16). I was at first inclined to the opinion 

 that the forms with the divided band were specifically distinct from those in 

 which it is not divided, but further study makes it probable that this is only 

 an individual variation. A similar splitting of the ciliated plate in its aboral 

 portion was observed by Heath in the Galapagos specimen. 



The epithelium of this ciliated band has essentially the same structure 

 in the two types of larvae. It is characterized by extremely small and com- 

 pact nuclei, which resemble the heads of spermatozoa, and by very long, 

 slender cell-bodies, every one of which starts from a nucleus and runs as a 

 fibril to the periphery of the epithelium and is then continued into the free 



