CEETATN STICHODACTTLIN^ TO THE MADEEPORARTA. 645 



mesentery. Traced below thej soon become rounded and bear 

 exactly similar elements — granular gland-cells, ciliated supporting 

 cells, and large nematocysts. Wiodactis and JRicordea, in like 

 manner, never display any trace of the Flimmerstreifen. In eacb 

 case tbe actual filameutal expansion is scarcely broader tban the 

 mesenterial epithelium, and passes more or less insensibly intc 

 it. On many of the well-developed mesenteries in Ricordet 

 florida there is no histological modification whatever suggestiv; 

 of a filament. 



Fowler (1886, p, 8) is inclined to regard the peculiar modifi- 

 cation met with in some of the mesenteries o1 Madrepora Burvillci 

 as representing the Plimmerstreif en. It is clear, however, that the 

 structures he refers to are but swollen parts of the mesenterial 

 endoderm. The cells are totally unlike the extremely narrow 

 ciliated cells of the Flimmerstreifen in the Actiniaria, and these 

 latter never contain zooxanthellse. 



Nematocysts. 



The assertion is usually made that the coral polyps are 

 characterized by much larger and more complicated stigmatic 

 cells than those of anemones. Thus Hertwig (18S2, p. 23), in 

 discussing the probable relationship between the CorallimorphidsB 

 and Corynactis, observes : — " Many might also consider as points 

 of affinity the fact that in both geuera {_Co7^allimorpJius and 

 Corynactis] the nematocysts attain an extraordinary size, that 

 both genera recall the skeleton-forming Zoantharia, and that 

 the nature of the mesoderm is the same in both." 

 ■ Nematocysts of more than one kind generally occur in the 

 same species, and though capable of development in almost any 

 region of the polyp, they are more usual in the tentacles, 

 stomodseal ectoderm, and the Driisenstreif of the mesenterial 

 filaments. Where acontia occur, as in the Sagartidse, the 

 nematocysts in them are somewhat larger. In coral polyps it is 

 usually the oval form which attains increased dimensions, and the 

 internal thread is but loosely spiral and often striated and 

 minutely spinous proximally. Such are best seen in the lower 

 region of the mesenterial filaments and in the stomodasal 

 ectoderm. 



A few anemones bear nematocysts comparable in size with 

 those of coral polyps. In the quotation given above, Hertwig 

 implies this to be the case in Corallimorphus and in Corynactis. 



LlJifjS'. JOURIf. — ZOOLOGY, VOL. XXVI. 46 



