154 SIDNEY F. HAEMER. 



replaced by a gelatinous matrix, in which lie connective-tissue 

 corpuscles. Are we not justified in assuming that the 

 "globules" are the active agents in the histolysis, and that 

 they are in fact typical phagocytes ? 



During the histolysis of portions of the anal cone, the latter 

 structure itself becomes much depressed. This feature of the 

 metamorphosis, although already obvious in fig. 9, may be 

 further illustrated by means of fig. 7, a section passing in a 

 plane corresponding to the line i j in fig. 16. 



Owing to the further depression (occurring at a slightly later 

 stage) of the anal cone, the marked bilateral arrangement of 

 this part of the vestibule is, in part at least, lost. At the stage 

 of figs. 8 and 9, as can be easily seen from these figures them- 

 selves, the posterior portion of the vestibule is no longer re- 

 duced in the median plane to a small slit between anal cone 

 and vestibular wall (as in fig. 1), but is, in this position also, 

 a spacious cavity lined by a columnar epithelium (fig. 9). 



After the anal cone has reached the condition of the latter 

 figure the vestibule, in sections parallel to the long axis of the 

 stomach, will usually appear bounded posteriorly by a simple 

 uniformly curved wall, whilst its oesophageal side is floored by 

 the degenerating tissue of the epistome (fig. 7). In later 

 stages, however, the well-developed epithelium of the sides of 

 the vestibule extends inwards, so that the cavity is then en- 

 tirely bounded by its permanent, partially regenerated epi- 

 thelium. 



In the next stage represented very considerable changes 

 have occurred, whereby the alimentary canal has taken up a 

 position not unlike that which it will ultimately retain. 

 Fig. 10 represents an actual section which passes in the median 

 longitudinal plane of a larva at this stage. Whereas in 

 fig. 16 the axis of the stomach is but slightly inclined to the 

 surface of attachment, in the present instance it has assumed 

 a position almost at right angles to this plane, and the con- 

 cavity of the gut is now directed towards the primitively pos- 

 terior end of the fixed larva. In the course of this rotation 

 of the alimentary canal the vestibule, owing to atrophy of one 



