Introduction to Animal ]\Iorphology . 1 13 



Fission may also occur, and may be imperfect, vertical, 

 producing caespitose, or horizontal, producing la- 

 mellar masses. Buds may also form, and may be 

 basogenic (from the base of the parent), stoloniferous 

 (from basal stolons), perigenic (from the sides of the 

 parietal coenenchyma), or calycular, arising inside the 

 cup of the parent. 



There are two sub-classes: — i. Zoantharia (Hex- 

 actinia) — having the mesenteries and simple, rarely 

 branched tentacles, in multiples of six (or five) ; the 

 former are in pairs ; some or all of them bear longitu- 

 dinal muscular bands (vanes) ; around the mouth is 

 often an annular canal communicating with the several 

 perivisceral spaces ; they are marine, and have no 

 central horny axis in their coenenchyma, except in 

 Antipathidae. 



Three orders are included: — i. Malacodermata — 

 sea anemones ; rarely colonial, with either no corallum 

 or a few spicules ; the body cavity is distended by 

 water, which can be expelled on irritation, causing 

 a rapid collapse ; the tentacles are numerous, the 

 sexes separate (except Sagartia troglodytes), the body 

 cylindrical, and the craspeda developed. They can be 

 multiplied by artificial division ; the embryos are 

 planuliform, then become ovate, and settling down 

 (sometimes in eight days), a mouth forms at the larger 

 end ; the wall of the digestive sac forms as a ring 

 around the mouth, which grows down into the body 

 cavity.* At first the tentacles are five or six, and the 

 mesenteries as many, but they increase in number 

 rapidly. They live for several years. One kept by 

 Daly ell for six years produced 276 young. In the 



* This is either a down growth or an invagination. 

 I 



