376 



ZOOLOGY 



SECT 



porite to near the border of the mouth is an S-shaped cylinder, 

 Ufie madreporic or stone-canal (Fig. 315, mad. can). The walls of 

 this canal are supported by a series of calcareous rings, and project- 

 ing into it is a ridge which bifurcates to form two spirally rolled 

 lamellae occupying a considerable part of the lumen of the canal. 

 In some Starfishes, such as Astropecten (Fig. 312), the internal 



FIG. 313. Anthenea flavescens. Upper view of a dissection of the internal organs. The 

 aboral wall of the body, with the exception of a small portion round the anus and the madre- 

 porite, has been completely removed. One of the five intestinal cseca has been removed with 

 the exception of its proximal part. All the ovaries have been removed except one pair, and 

 four of the pairs of pyloric caeca have been cut away close to their bases. 1 5, the five rays 

 with their ambulacral ridges ; amp. ampullae ; an. anus ; int. ccec. intestinal cseca ; i. p. cut 

 ends of the inter-radial partitions ; mad. madreporite with the madreporic canal ; ov. ovaries ; 

 pol. yes. Polian vesicles ; pyl. ccec. pyloric caeca ; retr. retractor muscles inserted into the 

 cardiac division of the stomach. 



structure is more complicated owing to the branching of the lamellae. 

 The interior of the madreporic canal communicates abov } with the 

 exterior through the grooves of the madreporite. At the bottom of 

 each of the grooves are a number of fine pores leading into vertical 

 canals of corresponding fineness, all lined, like the grooves and the 

 madreporic canal itself, with long cilia : most of these ope a below 

 into a dilatation of the madreporic canal, some into the ax ; al sinus 

 referred to below. Below, the madreporic canal opens into a 



