132 ACTINOZOA. 



ages, the * peristomial space,' is usually observ- 

 able. 



The mouth is of a slightly elliptical form, a 

 pair of tubercles, including between them a 

 groove, being situated at each of two opposite 

 points of its circumference. The stomach, or 

 digestive sac, into which the mouth directly leads, 

 is a short, distensible tube, open at both ends, 

 and extending about half-way towards the base of 

 the animal ; in diameter scarcely exceeding the 

 mouth itself, with which its form, when viewed 

 from above, is seen to correspond. The folds, or 

 grooves, between the oral tubercles are continued, 

 in the form of semi-canals, along the inner surface 

 of this stomach, until, finally, they reach the wide 

 aperture by which it communicates with the so- 

 matic cavity. 



A transverse section of the body of Actinia 

 exhibits two concentric tubes, the outer being 

 constituted by the body-wall, the inner by the 

 digestive sac. The wide space which intervenes 

 between these tubes is divided by a number of 

 radiating partitions, or ^mesenteries,' arising at 

 definite intervals from the inner surface of the 

 body-wall. The 'primary,' or first-formed and 

 widest, mesenteries serve to fix the stomach in its 

 place, their inner edges being inserted throughout 

 the entire length of its outer surface. From the 

 base of the stomach, the inner edge of each me- 

 sentery, becoming free, arches, at first, abruptly 

 outwards, and then, more gradually, downwards 

 and inwards, until at length it reaches the centre 

 of the base, from which all the primary mesen- 

 teries appear to radiate. Other partitions, de- 

 veloped in successive cycles between those just 



