ACTINOZOA. 137 



digeptive sac does not differ, in any essential respect, 

 from that of the column, than which it is much 

 thinner and more delicate, its endoderm being 

 richly furnished with cilia. Ordinary pigment 

 granules are here absent, but in their stead occurs, 

 within the upper portion of the stomach wall, a 

 thin layer of a red or yellowish brown tint, to 

 which some writers have ascribed the function of 

 a liver. The mesenteries are to be regarded as 

 processes of the column wall. The thin layers of 

 endoderm which invest the two sides of each 

 mesentery are produced beyond its free edge to 

 form the sac-like covering, within which the repro- 

 ductive elements are lodged. Having enclosed 

 these, the two layers are brought into mutual con- 

 tact, a narrow band being thus produced, to which 

 the cord-like craspedum is attached. 



The flower-like appearance of the fully expanded 

 Actinia is sufficiently familiar to every sea-side ob- 

 server. While the animal is in this condition any 

 passing object likely to serve as food is firmly 

 grasped by one or more of the tentacula, which, 

 aided by the muscular contractions of the body 

 wall, soon force it into the interior of the digestive 

 sac. The morsel thus swallowed is usually, after 

 a time, rejected by the mouth ; while the nutritive 

 matters withdrawn from its substance by the action 

 of the stomach secretions are transferred to the 

 somatic cavity, within which, as in the Hydrozoa, 

 the process of nutrition is completed. Of the 

 voracity of the Actinia many amusing accounts 

 have been made known. It may, nevertheless, be 

 kept in captivity for several months, if supplied 

 with water containing minute particles of organic 

 matter. 



