109 



Notes on a Slide, showing Ten Sections of the Oral disc 

 and Tentacles of Cerianthus Solitarius. 



By Arthur Pennington. 



{Read November 28th, 1884.) 



Upon the slide accompanying these notes is a series of longitu- 

 dinal sections of the oral disc of C. solitarius, carried down so as to 

 show the septa and a portion of the body-wall. The sections are 

 cut at right angles to the diameter of the animal, a mode of catting 

 which possesses the advantage of showing more than would a longi- 

 tudinal section cut in any other manner. 



Eecent observers have separated the Cerianthidce from the other 

 anemones and made them into a distinct family or tribe, in conse- 

 quence, mainly, of the fact that the septa or mesenteries, which are 

 such important features in the organisation of the Zoantharice, are 

 not paired or arranged in cycles as in the Actinia?, nor confined to 

 the limited number of eight as in the Edwardsice. 



There are only three defined species of the genus Cerianthus, one 

 of which, C. Lloydii, is found in England. The specimen of C. 

 Solitarius, from which the sections on this side were cut, I obtained 

 from the Naples Zoological Station. 



The specimen was stained with hasniatoxylin, and mounted, after 

 the sections were cut, in Canada balsam. Before cutting the sec- 

 tions the animal was imbedded in paraffin. 



The sections on the slide exhibit clearly the division of the body 

 structure of the anemones into the three layers, ectoderm, meso- 

 derm, and endoderm. The deeply coloured central layer is the 

 mesoderm. The layer exterior to this, and evidently of more com- 

 plicated structure, is the ectoderm, and the internal layer is the 

 endoderm. The septa will be seen to possess only two of these 

 layers, namely, the central mesoderm lined on each side with endo- 

 dermal cells ; the tentacles possess all the layers. 



The ectoderm may be clearly made out to contain three distinct 

 layers, namely, epithelial, nervous, and muscular. The epithelial 

 cells form the broadest layer ; next the nervous layer may be seen 

 as a fine band of lighter cells, and deeper still lies the muscular layer, 



