394 E. A. SCHAFER. 



doubtful by tlie important observations of Mr. Watneyi on 

 intestinal absorption, which he has shown to take place, not 

 through the epithelium itself, but by pseudo-stomata formed 

 by processes of connective-tissue-corpuscles, which project 

 between the epithelium, with which they are never anato- 

 mically continuous. 



We have, then, in the case of endothelium, not only an 

 undoubted mesoblastic origin, but a close relationship with 

 connective tissues ; its cells, moreover, never form glands 

 nor secrete. Epithelium, on the other hand, has a doubtful 

 derivation from the mesoblast ; gland-formation and secretion 

 are among its most constant and striking characteristics, 

 and it has absolutely no relationship with the connective 

 tissues. Notwithstanding, therefore. Dr. Foster's statement 

 (p. 292) that, " In short, there is no reason why the cells 

 spoken of as forming endothelium should have a common 

 title, distinct from the general term epithelium," I must 

 confess that I am not convinced, but think that the reasons 

 I have given above are sufficient to render the use of sepa- 

 rate terms at least opportune — " im Interesse physiolo- 

 gischen Verstandnisses." 



Description of an Apparatus 2 ybr Maintaining a Con- 

 stant Temperature under the Microscope. By E. A. 

 ScHAFER, Assistant-Professor of Physiology in University 

 College, London. 



The necessity of having the means of conveniently, but at 

 the same time accurately, maintaining objects, especially the 

 living tissues, under observation at a uniform temperature 

 (generally that of the body) becomes more obvious every day. 

 The existing methods of effecting this are, as a rule, not 

 sufficiently accurate for exact investigations ; and, on the 

 other hand, the more accurate modes are frequently in- 

 convenient of application. For example, the apparatus 

 described by Strieker and Burdon-Sandersou in this Journal 

 for 1870, — although it is possible by its aid to maintain 

 a constant temperature under the microscope for a con- 

 siderable time, — yet requires that there should be a vessel 

 of water constantly boiling near the observer, and that 

 the water in this vessel should be maintained at a uni- 

 form level, necessitating a supply tube from a cistern, and 



' ' Proc. Roy. Soc.,' vol. xxii, p. 293. 



* Made for me by Mr. Casella, of 147, Holborn Bars. 



