1893.] and Functions of the Alimentaiy Canal o/Daphnia. 47 



Sometimes the border contains a number of small clear non- 

 staining patches oval or irregular in shape, generally close to the 

 base of the border; these are commonest opposite the intervals 

 between ceils. 



The borders of adjacent cells are generally in contact and 

 closely adherent. In cases where the cells are at all displaced 

 the borders may be seen stretched out and still adherent. The 

 border is therefore fairly tough and of course extensible as it 

 changes in shape with the alterations in form of the cell bodies. 



The mobility of the rods and of the hyaline substance of the 

 border is thus very obvious in Daphnia, and Heidenhain has 

 attributed a similar mobility to the hyaline border of the cells 

 lining the small intestine of vertebrates*, and parallel changes 

 have been noticed at times in the ciliated cells of the gut of 

 Lumbricus-f-. 



Actual measurements show that the depth of this border forms 

 a greater proportion of the total depth of the cell in the diverticula 

 and anterior portions than in the rest of the gut. Thus in one 

 case the measurements were : 



Diverticula 



Anterior region of intestine 



Middle to posterior region 



Depth of cell body. Depth of border. 



5/jb 

 lO/ii 



7'0/jb 



6-7/a 

 3/i 



Thus we may say generally that the border is best developed 

 in that region in which the absorption of fat was found to take 

 place, and this corresponds to observations made in other animals. 

 Thus in vertebrates the hyaline border is best developed on the 

 cells of the villi of the small intestine, and in Lumbricusj it, or 

 rather its homologue, is only found on those cells which ingest fat. 



Just posterior to the junction of the stomodseum with the 

 mesenteron, there is a short neck-like region in which the lumen 

 is smaller and the cell border lower in proportion to the depth of 

 the cells than in regions before or behind. 



If we turn to the histological characters of the cell substance 

 of the cells lining the mesenteron we obtain further evidence of a 

 differentiation of the epithelium into regions corresponding to 

 those which actual observation of the processes of digestion shows 

 to exist. 



The cells of the middle region of the mesenteron are specially 

 characterised by the presence under certain conditions of granules 



* Heidenhain, Pjlilger's Archiv. Bd. xliii. Suppl. 



t M. Greenwood, Journ. of Physiol. Vol. xiii. p. 239. 



X M. Greenwood, loc. cit. 



