150 SIDNEY F, HARMEU. 



appear, so that the oral grooves are not distinguishable in the 

 post-anal region of the vestibule. The above description, 

 together with a reference to fig. 5, will thus show that the deep 

 post-anal groove (m. v.) of fig. 1 is continuous equally with the 

 oral grooves and with the general vestibular cavity. For 

 further clearness, dotted lines in the same figure indicate the 

 position and relations of the right lateral fold as it would appear 

 by looking at the wall of the vestibule from the inside of the 

 latter. The relations of half of the ciliated ring and of the 

 right oral groove are also shown in the figure. 



Fig. 2 represents a longitudinal section of a recently-fixed 

 larva, passing in the direction of the line c d in figs. 3 and 4. 

 One of the lateral folds, owing to its projection inwards into 

 the vestibule, separates the latter into two portions, containing 

 respectively the mouth (and oral groove) and part of the epis- 

 tome. The latter portion obviously corresponds to one of the 

 lateral regions of the vestibule (/. v.) in fig. 3. Fig. 2 further 

 explains the continuity of the tip of the epistome with the 

 lateral folds (cf. figs. 1 and 5). In more median sections of 

 the same series the latter are not seen, the epistome being per- 

 fectly free at its apex, whilst the separation of the vestibular 

 cavity into two parts is not apparent. 



A considerable portion of the base of the epistome and of 

 the sides of the anal cone is formed of a remarkable tissue, 

 composed of large cells, with transparent contents, hardly 

 staining with colouring matters (fig. 2, x). The nature of 

 this tissue (which atrophies during the metamorphosis) is 

 unknown to me. 



The revolution (about to be described) of the alimentary 

 canal was obviously well understood by Barrois, although I 

 did not formerly succeed in making out his exceedingly con- 

 cise statements on this head. 



Figs. 8 and 9 represent two sections of an obliquely longitu- 

 dinal series through a more advanced stage. Fig. 9 involves 

 the rectum, whilst fig. 8 shows the mouth and oesophagus. In 

 the latter figure is seen one of the deep portions of the vesti- 

 bule lying at the sides of the rectum, which is itself of course 



