118 COMPARATIVE ANATOMY. 



canals in the Beroi'das and CallianiridaB pass into a circular canal at 

 the oral pole. In the latter, two canals, which run along the sides of 

 the wall of the stomach, and which come from the funnel, also enter 

 the circular canal. In the Cydippidas, these are very wide, and 

 appear to form a common space around the stomach. Finally, two 

 shorter canals, which do not pass directly from the funnel, but 

 from the canals derived from it, run outwards and open by pores, 

 which can be closed, at the sides of the polar areas (cf. p. 111). 

 They are placed diagonally, and provide the gastrovascular system 

 with a second means of communication with the surrounding 

 water. 



The form of the body leads to various modifications in the 

 arrangement of this system of canals. The various groups of canals 

 may be branched. Thus, in the Beroidae the radial canals form 

 lateral branched diverticula, which are present, though they are 

 not so large, in the other forms, and are in connection with the 

 generative apparatus. 



§ * 



o 



In some divisions of the Acalephas there are filamentous structures, 

 which project into the central cavity of the gastrovascular system ; 

 they are called Gastric filaments (and, though less appropriately, 

 mesenteric filaments) . They are found for example in the LucernaridaB 

 and Discophora. In the latter they form tufts of filaments, placed in 

 diverticula of this cavity, and execute vermiform movements. They 

 have similar characters in the Lucernaridas, but are different in the 

 Anthozoa. In the Anthozoa pad-like processes, richly provided with 

 stinging cells, run along the free edge of each septum, turned towards 

 the gastric cavity ; they seldom become filamentous, and are some- 

 times limited to two of the septa (Tubipora). Nothing is known 

 as to the function of these organs, which are differentiated very 

 early. 



Although glandular organs do not seem to be differentiated in 

 the digestive cavity of the Ccelenterata, yet there is an arrangement 

 which should be noted here ; it may be regarded as an indication of 

 a secreting system, perhaps analogous to the liver of higher animals. 

 It is this, namely, that the epithelial investment of the stomach, 

 which is present in many Ccelenterata, is distinguished by its peculiar 

 colour. The pigmented cells are set longitudinally, and are generally 

 placed on the projecting folds of the wall of the stomach in the 

 Anthozoa; they are also developed in the Hydromedusaa, even in 

 the polyp forms (e.g. Tubularia)) ; in the Siphonophora they form 

 distinct pad-like longitudinal rows at the base of the digestive 

 cavity of the nutrient individuals. A network of " hepatic canals," 

 attached to the single large stomach of the Velellida), appears to 

 be specially differentiated ; it is found on the under surface of the 

 disc. 



