MORPHOLOGY OF THE AMPHlNEURA. 219 



(4, 1 , 10, 23) have at least succeeded in discovering any trace 

 of it. 



The slit in the pharynx of Proneomenia which gives access to 

 the small radular csecum, at the same time serves to evacuate 

 the products of two long cylindrical parallel glands, situated under 

 the intestinal epithelium, which converge towards this slit. 

 These glands are regarded as salivary glands (7). They are 

 absent in Keomenia ; nor has anything of the sort as yet been 

 noticed in Chcetoderma. In Chiton salivary glands have been 

 described (16), but these would appear to occupy a dorsal posi- 

 tion with respect to the pharynx. Whether the latter are never- 

 theless comparable to those of Proneomenia, or whether we shall 

 rather have to look upon the so-called pharyngeal sacs (Schlund- 

 sacke, Middendorf) as the homologue of the tube-shaped 

 glands of the latter genus, will have to be inquired into carefully. 

 The part of the intestine which follows upon the pharynx is 

 simplest in Neomenia and Proneomenia. In both genera it occupies 

 the greater part of the space available within the muscular tunic 

 after deduction of the genital gland. It is straight, and on both 

 sides provided with very deep folds, which might be compared 

 to as many (hepatic) caeca. Ciliation has been noticed along the 

 median ventral and dorsal line. The rectum, which posteriorly 

 passes below the pericardium and in the midst of the renal and 

 genital excretory ducts, is narrowed and provided with cilia all 

 over the surface. 



In Chcetoderma a subdivision of this part of the intestine has 

 taken place, which appears to me to be very well interpreted by 

 Hansen (6), who regards the posterior caecum-like portion, 

 opening out into the principal cavity, which is terminated by 

 the mouth and anus, as the incipient stage of a separate liver. 

 This stage has been very far surpassed in the Chitones, where 

 the more or less primitive intestinal arrangement of the Soleno- 

 gastres is replaced by an intestinal tract, which is comparatively 

 narrow, considerably bent upon itself and coiled, and into which 

 a well' separated, dendritically-shaped liver opens. On this 

 head the difference between the two subdivisions of the Amphi- 

 ^JEURA is, as may be seen, considerable. 



Only in the Chitons the posterior opening of the rectum 

 opens directly to the exterior ; in Neomenia and Proneomenia 

 its contents are first evacuated, together with those of the excre- 

 tory and genital organs, into a sort of common cavity or cloaca, 

 the external opening of which serves for both systems. In 

 Chcetoderma there is no true cloacal cavity, but. the infundibulum 

 into which the rectum and the nephridia open, and in which the 

 branchiae are placed, nevertheless has a certain analogy with it 

 (fig- 8). 



