18/6.] MUCOUS MEMBRANE IN KANGAROOS. 175 



of the tissue, and the limit of their distribution can be readily made 

 out. They are seen to be absent, near the orifices of the glands, 

 where the tubes are lined with columnar epithelium. 



The relation of the peptic cells to the central cells is best seen in 

 the horizontal sections (as in fig. 8, which is taken from the Dorcop- 

 sis stomach). Here the peptic cells (p, p) lie immediately outside 

 the central cells (c, c) (which almost fill up the tube, leaving but a 

 very small lumen) and in close contact with them. But in Macropus 

 the contact is not so close ; for the basement membrane of the gland 

 sends horizontal lamellar projections inwards, partially surrounding 

 the spheroidal cells and separating them more from the central ones. 



It can be clearly made out (both in vertical sections showing the 

 glands along their whole length, and in sections carried obliquely 

 across them so that in different parts of the section different 

 levels of the tubes are cut) that the central cells are directly con- 

 tinuous at the neck of the glands with the gradually shortening 

 columnar cells of the gland-mouth, and resemble, therefore, in this 

 respect the cubical cells which line the greater part of the tubes of 

 the second region*. In general aspect too the central cells resemble 

 those ; but they are for the most part, as before mentioned, smaller 

 and more angular and closely packed. This is especially the case 

 at the base of the gland, where the cells almost entirely fill the tube 

 so as to leave little or no lumen (fig. 9). 



Transition between the Second and Third Regions. — The line 

 of demarcation between these is best marked, as before stated, in 

 Dorcopsis, where there is a slight furrow between them, the 

 mucous membrane increasing rapidly in thickness on the peptic 

 side of the furrow. A section across the line and including a part 

 of each region, is shown in fig 10, as seen under a low power in a 

 preparation stained with aniline blue. The glands of the second 

 region become gradually shorter until opposite the bottom of the 

 furrow, where they are shortest ; those beyond rapidly increase in 

 length, but exhibit at first exactly the same structure. At about 

 the third or fourth row, however, a few peptic cells become super- 

 added to the others about the middle of the glands ; and these 

 increase in number and occupy a greater length of the gland as we 

 proceed further into the third region, until after a few more tubes 

 they are found throughout the greater part of the length of the 

 glands ; so that from a study of the mode in which the two kinds 

 of glands pass into one another, as well as from a comparison of 

 their structure, it is clear that the main parts of the glands of both 

 regions are almost precisely similar and will probably have a similar 

 function, and that the only difference of importance lies in the fact 

 of the superaddition of the peptic cells in the glands of the third 

 region — probably implying the superaddition of some other function 

 in these glands. Whether this, as is generally believed, is the elabo- 



* Strictly speaking, these cells are not cubical ; for although they appear so 

 when the glands are seen longitudinally, they must of course, as seen in a trans- 

 verse section of the glands, become narrower towards the lumen; so that the 

 shape of each cell is in reality that of a truncated wedge. 



