22 E. A. Schäfer, 



2. That some of the lymphoid cells wMcli are found so numer- 

 ously in the tissue of tlie intestinal mucous membrane may 

 liave been derived by emigration from the bloodvessels is a 

 proposition which it would be difflcult absolutely to controvert, 

 especially since such emigration occurs in other parts of the 

 body. But that it shoiüd take place to any great extent is 

 rendered unlikely by the fact that in sections of the miicoiis 

 membrane the lymph-corpuscles are not found to be especially 

 numerous either within the bloodvessels or in the tissue 

 immediately surrounding tliem. Indeed few white corpuscles 

 are seen in the vessels nor have I ever been able to observe 

 in the sections a Single leucocyte fixed in the act of passing 

 out from a bloodvessel. 



3. The third possibility, namely that the wander-cells which 

 migrate from the epithelium towards the lacteals are directly 

 derived from the epithelium-cells by the division of the latter, 

 is one which would I imagine be scouted as improbable by 

 most physiologists. It is not however so unlikely as it appears 

 at first sight. For as already noted (page 10) there is di- 

 stinct evidence that the columnar epithelium cells do normally 

 undergo division, for they exliibit here and there characteristic 

 karyomitoic changes ; and although it is usually assumed that 

 the result of such division is the production of new epithelium 

 cells, which may serve to take the place of old cells that have 

 been thrown off, the fact that such removal of the epithe- 

 lium-cells occurs normally has never been substantiated, but 

 is purely hypothetical. On the other band the consideration 

 of certain facts in comparative embryology appears to lend 

 a considerable amount of probability to this view of the origin 

 of these migratory cells. For it has been shown that in 

 many invertebrate animals') and also probably in vertebrates*) 



') As in Holothuria as described by Selenka (Zeitsehr. f. wisseiisch. Zoologie, 

 XXVn, 1876). 



*) In the chick according to Balfour (Comparative Embryology); and in the 

 mammal according to Heape (Development of the moie. Qnart. Journ. of Microsco- 

 pical Science, July 1883). 



