210 ARTHUR WILLEY. 



intra-buccal orifice (8), and in the present paper the account 

 of its atrophy. It arises in an embryo with nine to ten pairs 

 of myoccelomic pouches^ as a ventral transverse fold of the ali- 

 mentary canal at a point intermediate between the first and 

 second myotomes. 



The fold extends up to the right side on the one hand^ and 

 ventralwards round to the left side on the other. It then 

 becomes separated throughout its whole length from the 

 alimentary canal, and develops an opening to the exterior 

 on the left side, just below the lower margin of the mouth. 

 Its intra-buccal orifice does not appear until a rather later 

 period. 



In striking contrast to all the other organs which adjoin it, 

 the club-shaped gland does not undergo any change of position 

 during what has been elsewhere called the process of symmetri- 

 sation (cf. figs. 4, 5, and 18). 



During Stage V the club-shaped gland commences to atrophy, 

 and towards the end of that stage it disappears altogether, the 

 intra-buccal orifice being the last to go. 



Considering their close proximity to one another, it would 

 be natural to suspect that intimate relations existed between 

 the club-shaped gland and the endostyle. 



I made a few observations which seemed to show that the 

 endostylar epithelium, at least before it has assumed its ventral 

 position, is extremely delicate and liable to disrupture. 



When a larva had been confined for a very short time between 

 slide and cover-glass, the epithelium of the endostyle would 

 commence to give off numerous small round homogeneous 

 ciliated bodies, which passed into the alimentary canal, and were 

 there apparently absorbed. 



This happened sometimes so soon after the larva had been 

 placed upon a slide that I did not recognise it at first as a 

 pathological phenomenon, as of course it was. 



The fact that the endostyle is such a highly specialised and 

 delicate (while young) structure suggests the idea that possibly 

 a collateral organ like the club-shaped gland (concerning the 

 morphology of which see below) might function as a sort of 



