INVERTEBKATA, CRYPTOGAMIA, MICROSCOPY, ETC. 467 



direct, so that they only pass during development into the supporting 

 lamellfe. 



The mesenterial filaments are shown not to have the same structure 

 in all tlieir parts, but to consist of a median portion (bands of urti- 

 cating glands) and of two lateral ciliated bands. Their structure is 

 dealt with in detail ; of their function it is thought that the median 

 portion is secretory and that the ciliated bands which are not present 

 on the lower portions of the filaments have a kind of circulatory 

 activity. These organs are very largely supplied with nerves. 



The acontia form the subject of the last division of this chapter : 

 these protrusible organs are not to be found in all species of Actiniae ; 

 but in Sagartia parasitica they form elongated filaments with a worm- 

 like movement which are distinguished by their white or feebly violet 

 colour from the yellowish mesenterial filaments ; quickly protruded, 

 they are but slowly retracted ; in structure they are much as Heider 

 has represented them to be, but the fact that their cells are modified 

 to form stinging cells and not glandular cells prevents our ascribing 

 to them any secretory function. 



Anatomy of Cerianthus.* — Many investigators have, of late, 

 directed their attention to one or other group of the Coelenterata ; 

 among these we have now to number Von Heider, who has investi- 

 gated the anatomical characters of C. memhranaceus. Directing atten- 

 tion to the nomenclature of parts, as suggested by himself, the wall 

 {Mauerhlatt), or column, is by him called the body-wall ; the disk, or 

 oral plate, the oral disk ; the stomach (Gasse) is named the oesopJiageal 

 tube ; and the tentacles may be marginal or oral; the arrangement of 

 the tentacles is described in some detail. 



To examine the internal structure, it is well to make a longitudinal 

 section, and to pin the cut edges ; if the creatui'e is kept in sea-water 

 it will long remain in a fresh condition ; its longitudinal axis will 

 indeed contract to about half its length, but the breadth will, in con- 

 sequence of the feeble development of the circular musculature in this 

 family, diminish very sliglitly. One great practical advantage of this 

 arrangement is tliat Ceriantlms does not break away from the needles 

 wliich hold it, so easily as do most of the Actinia3. Macroscopic exa- 

 mination now reveals the following arrangement of parts. The oeso- 

 phagus extends from the oral tentacles about two centimetres down- 

 wards, and ends by a free margin in the body cavity. Two white 

 grooves (the gonidial grooves of Gosse) become apjiarent, and these 

 are looked upon by the author as the signs of tho primitively bilateral 

 arrangement of the parts of an Actinian. These two grooves differ 

 considerably in character ; one is very distinct, tho other seems often 

 to bo hardly present. From tlio inferior edge of tho fcsophageal tube, 

 wliich is always more briglitly coloured, tho inner margins of the now 

 free septa pass downwar<ls as continuations of tho parallel grooves 

 seen on tho (esophageal tube. These septa may be arranged in three 

 groups : — 



(1) ContiiiHous Septa.— Thin nanio is applied to the 2>air of septa 



* ' SD. Iv. Akiid. Wusa.' (Wicn), Ixxix. lat sec. (1879) p. 204. 

 VOL. III. 2 II 



