244 SIDNEY F. HARMBR. 



plication, their protoplasm being finely granular and staining 

 readily with colouring matters. The backward growth of the 

 vestibule occurs first in the regions at the two sides of the anal 

 cone (cf. fig. 3), but soon extends to the median portion be- 

 hind the cone (fig. 9), so that this part of the vestibule grows 

 towards the free end of the fixed larva, during the rotation of 

 the alimentary canal, as a single actively extending diverticu- 

 lum, in which the primary difi'erentiation of median and lateral 

 regions is no longer marked. 



Fig. 6 will serve to explain more clearly the relations of the 

 oral grooves and neighbouring structures at a stage very slightly 

 earlier than that of figs. 8 and 9. The section passes in a direc- 

 tion corresponding to the line k l in fig. 16, and consequently 

 involves the apex of the epistome, the lateral folds, and the 

 oral grooves. The anal cone, visible in fig. 5, is, of course, not 

 involved by the section, which in other respects differs from the 

 former figure mainly in the facts that the diameter of this por- 

 tion of the vestibule has become lessened, and that by the par- 

 tial rotation of the alimentary canal the apex of the epistome 

 has come nearly into contact with the posterior wall of the 

 vestibule (the manner in which this happens will be understood 

 by comparing fig. 1 with fig. 16), the form of the lateral folds 

 being at the same time altered (cf. fig. 6 with fig. 5). By this 

 change of position of epistome and lateral folds, the oral and 

 anal sections of the vestibule communicate merely by a com- 

 paratively small round aperture. The oral grooves are no 

 longer continuous posteriorly with the anal portion of the 

 vestibule, although on the left side of the section at least, a trace 

 of the former continuity is distinguishable. During later stages 

 the growth of epistome and lateral folds completely separates 

 the oral from the anal division of the vestibule, the aperture 

 a. V. V. in fig. 6 being gradually constricted until it finally 

 disappears. 



At the stage of figs. 8 and 9 a considerable amount of his- 

 tolysis is taking place. This process aflFects specially the 

 stomach, the epistome, the anal cone, and the ventral portion 

 of the vestibule. In the case of the stomach, portions of the 



