A NOTE ON ENDOTHELIUM. 391 



cavity and mouth, but the gastrula-stomach and orifice 

 of invagination ; the latter closes up, and the pedicle so 

 formed becomes the rectum, which terminates blindly. 



E. With a good English quarter, or, better, with Hartnack's 

 10 immersion, and the use of osmic acid, the cilia which 

 cause the rotation may be seen. They are disposed on an 

 annular band, the commencing velum. 



F. The annular ridge has nothing to do with the mantle's 

 margin, but is the velum. 



G. The new in-sinking has no connection with the anus or 

 rectum, which latter already is taking shape in the pedicle 

 of invagination. It is the " shell-gland," a structure com- 

 mon to many embryo mollusca, but hitherto unrecognised. 



H. The so-called large yelk-spheres are not now first 

 formed, but have been there all the time, forming the wall of 

 the invaginated gastrula-stomach. They now undergo im- 

 portant segregative changes, and present the appearance of 

 large clear globules, covered in by a fine granular reticulum. 



I. The alimentary canal is from the first bent, the csecal 

 termination of the rectum lying a little forward, and not 

 opposite the mouth. 



J. The shell, as an exceedingly delicate membrane on the 

 surface of the shell-patch (in the centre of which lies the 

 shell-gland), is observable long before this. 



K. The mouth never pushes forward, but rather becomes 

 sunk and enclosed by the increasing development of the 

 border of the velum, where it overhangs the mouth. This 

 part of the velum forms the subtentacular lobes of the 

 adult. 



L. It can be seen at a very much earlier period. 



A Note on Endothelium. By John Cavafy, M.D., 

 Assistant-Physician and Lecturer on Physiology at St. 

 George's Hospital. 



In the last number of this JournaP there is a paper by 

 Dr. M. Foster, " On the term Endothelium," in which he 

 gives various reasons against the further use of this word in 

 histological terminology. He objects to the word, both 

 because its etymology is " of the most grotesque kind," and 

 also on far more important anatomical grounds. 



Much that is brought forward by Dr. Foster is, doubtless, 

 true ; but some portion of his statement must, I think, he 



' 'Quart. Joum. of Mic. Sci.,' 1874, p. 219. 



