144 



ACTINOZOA. 



ments 



face the flattened sid es of the mouth. The acces- 

 sory actinomeres, slightly narrower than either of 

 the preceding, serve to occupy the four inter- 

 spaces which occur between the lateral and an- 

 tero-posterior pairs. 



The lateral actinomeres are further distinguished 

 by the presence in each of a large sac, which opens 

 obliquely, outwards and downwards, about mid- 

 way between the equatorial region and the apical 

 pole of the body. From this sac the animal has 

 the power of protruding at pleasure a long, highly 

 contractile, beautifully fringed, tentacle. 



Immediately within the apical pole is situate a 

 peculiar body, supposed to be an organ of sense, 

 which is best termed the < ctenocyst.' Upon this 

 rests a nervous mass from which issue small fila- 



The structure of these parts, as also of 

 the prehensile, locomotive, and reproductive appa- 

 ratuses are described in their appropriate para- 

 graphs. At present let us chiefly notice, in con- 

 nection with the form of the body, the arrange- 

 ment of its somewhat complex nutrient system. 

 {fig. 27.) 



This system may be said to commence in the 

 stomach, or digestive sac, a cavity having the 

 general form of an elliptic cylinder, and extending 

 from the mouth through the longitudinal axis 

 of the body, for about -6 of its entire length. 

 Slightly contracting below, the digestive sac is 

 seen to open into a much wider and shorter cavity, 

 also axial in its direction, known as the ' funnel,' 

 which gradually diminishes in diameter as it ap- 

 proaches the apical pole of the body, to terminate 

 just above the ctenocyst and nervous mass. From 

 the funnel three pairs of canals are given off. 



