15 



glands, symbiotic algoe, and nccumnlations of reserve 

 material to be nsed in tlie regeneration of injured arms 

 or pinnules. The value of the last view is somewhat 

 vitiated by the fact that sacculi do not occur in the allied 

 genus Actinometra, in the injured arms and pinnules of 

 which regeneration goes on quite as actively as in those 

 of Antedon. The present writer is inclined to regard the 

 function of the sacculi as excretory. 



Digestive System. 



The aperture of the mouth does not occupy the centre 

 of the disc, but is more or less displaced in the direction 

 of the anterior radius (PI. II., fig. 24, mth.). It opens into 

 a gradually widening resophagus, which runs obliquely 

 in the direction of the right posterior radius, and there 

 expands into a large sacculated intestine (PI. II., fig. 23, 

 int.). This, descending towards the aboral face of the 

 visceral mass, and gradually narrowing, makes a complete 

 coil around the vertical axis of the disc in the direction 

 of the hands of a chx*k. On re-entering the posterior inter- 

 radius it ascends the anal funnel and opens to the exterior 

 through the anal aperture. In addition to numerous 

 short diverticula which open into the intestine in the 

 first third of its course (fig. 23), there are two long 

 ones with finely-branched extremities, which open upoii 

 its inner border in the neighbourhood of the left anterior 

 radius (fig. 23, div.). The alimentary canal is of almost 

 uniform structure throughout. It consists of an 

 epithelium of fusiform, ciliated cells interspersed, in the 

 (psophagus, witli caliciform cells (PI. II., fig. 25), and, 

 throughout its length, with very minute rounded cells, 

 especially between the basal ends of the fusiform cells. A 

 layer of nerve fibres, continuous with the sub-epithelial 

 nerve ring, underlies the (esophageal epithelium and 



