24 



longitudinal rugae. The vast collection of glands would indi- 

 cate important secreting functions. Behind is a remarkable 

 lingual organ, which in longitudinal section resembles the 

 tongvie in mammals. It is attached at the base posteriorly to 

 a dense glistening muscular mass, separated by a layer of hori- 

 zontal fibres from the complex series of radiating muscles which 

 diverge upward to the periphery of the organ. In vertical 

 longitudinal sections in the middle line, these interwoven fibres 

 posteriorly are separated, by septa passing downward from the 

 thick chitinous coat, into spaces which enlarge anteriorly. The 

 muscles at the tip of the tongue arch backward over the posterior 

 part of the preceding glandular region (which forms a high 

 vascular cushion), and pass downward to the front of the dense 

 basal glistening mass formerly alluded to, the curve of the arch 

 becoming less and less till the fibres are nearly vertical behind 

 the cushion, or at the commencement of the smooth and dense 

 cuticular region of the tongue. The chitinous coat of the organ 

 is so largely developed at this part that it is as thick as the 

 hypodermic layer. In this region also are three strong plates of 

 transverse muscular fibres extending from summit to base. If 

 the section deviates to the lateral regions, the decussation of 

 the fibres is very complex. In transverse sections, again, near 

 the tip, the thickness of the hypoderm on the rug^s of the pre- 

 lingual mass as well as in the lingual papillae is considerable. 

 In the centre of the tongue is an inextricable mass of crossed 

 and interwoven fibres, the base assuming a somewhat stratified 

 appearance, since the blood-vessels lie at intervals in regular 

 horizontal rows. The tip of the tongue is highly vascular, 

 indeed, the organ throughout is richly supplied with blood- 

 vessels. The dorsum of the free tip is covered by a series of 

 elevated papillae — truncated at the tip, and with one angle 

 pointed. They are processes of the hypoderm sheathed in cut- 

 icle. Nothing can exceed the complexity of the muscular 

 structure of this organ, which is eminently calculated to sub- 

 serve important functions. Probably the animal erects its lingual 

 process and applies it with a rasping action to the surface of a 

 sponge, the successive pieces being crushed against the firm 

 rugose wall behind, by the hard posterior surface of the tongue, 

 and again subjected to the play of the deeply folded or lamellar 

 region behind it. Before the food reaches the intestinal surface, 

 it has been partially disintegrated and litted for absorption, 

 especially soft tissues like those of sponges. Minute shells of 

 annelids, such las Spirorbis, are of course less affected, though 

 many are broken into fragments, and all are in a condition to 

 give up their contents. 



Behind the tongue the alimentary canal presents on its 

 ventral aspect a large and a small fold, the former in longitudi- 



