STOMACH AND INTESTINE. 



323 



They everywhere bound a tube with a dis- 

 tinct calibre. 



In the cardiac region, it is only the ridges, 

 and the upper part of the tubes, which are 

 covered by columnar epithelium. At the 

 first (B b, fig. 24-8.) or second bifurcation of 

 the primary tube, the character of its lin- 

 ing altogether changes : and from hence 

 onwards to their rounded blind extremities, 

 the secondary tubules are immediately lined 

 by peculiar oVal cells (B c, fig. 243.). These 

 cells are analogous to those seen in the 

 human stomach. They differ however from 

 them, not only in their great size, and more 

 distinct walls," but also in the fact, that they 

 generally bulge the basement membrane of 

 the tube, so as to give it a somewhat moni- 

 liform outline. A closer examination shows 

 this appearance to be caused by the prominent 

 cells occupung irregular heights around the 

 wall of the tube. 



On getting the middle of such an isolated 

 tube into the focus of the microscope, we find 

 tiiat in the higher part of the tuDule, near 

 where it opens into the primary tube, the 

 oval cells, which are always in immediate 

 contact with the basement membrane, form a 

 double row with a somewhat sinuous interval. 

 This interval is a distinct though narrow 

 calibre. Below this visible calibre, I had 

 long been aware that the similar interval 

 between the larger cells was occupied by an 

 immense number of small nucleated cells or 

 cytoblasts, many of which are firm, with dis- 

 tinct and somewhat angular outlines; while 

 others are excessively delicate, pile, flattened, 

 oval, transparent, and of equal or much smaller 

 size. And the more skilful manipulation of 

 Koelliker has recently enabled him to state, 

 that the centre of the tube presents a con- 

 tinuous narrow calibre or cavity (-*,/#. 249.), 

 which is immediately bounded by these small, 

 roundish, or angular cells (c, A and B). Be- 

 tween these small cells and the limitary mem- 

 brane, the large oval cells are interposed 

 (b, A and B). Bt?low, the latter often seem to 

 form the sole contents of the tube. 



The truth of Koelliker's description I can 

 fully substantiate ; so far as regards the upper 

 part of these secondary tubes, in the cardiac 

 five-sixths of the organ. Even the blind ex- 

 tremities of the tubes seem to have their 

 axes occupied by the delicate cytoblasts pre- 

 viously alluded to ; but they are here, so far 

 as I can see, disposed irregularly. Higher up, 

 the cells are more angular, and possess more 

 distinct outlines; and are often arranged in 

 two rows, which are in contact at the centre 

 of the tube. It is only towards the apertures 

 of the secondary tubes," where the oval cells are 

 beginning to be more thinly scattered prior 

 to their disappearance, that these small cyto- 

 blasts appear to form a distinct calibre or 

 tubular cavity of appreciable width. Here 

 they merge into the columnar form; a change 

 which begins by their becoming elongated to- 

 wards the axis of the tube, and allowing water 

 to develope a distinct cell-membrane at this 

 part (c,Jig. 249.). But there are many appear- 



ances which render it by no means impossible 

 that the whole length of the tube possesses a 

 narrow calibre, formed by a regular arrange- 



Fig. 249. 



Portions of tubes from the cardiac extremity of the 

 dog's stomach. Magnified 350 diameters. (Partly 

 after KoeUiker.) 



A. portion from the middle of such a cardiac 

 tube ; a, limitary membrane of tube ; b, large oval 

 gastric cell ; c, smaller axial cells. B. Same seen 

 in transverse section ; a, b, c, as above. External to 

 c are seen indistinctly some delicate cytoblasts ; c, 

 junction of the primary and secondary tubes, show- 

 ing the mode in which the small axial cells of the 

 latter are continuous with the columnar cells which 

 form the epithelium of the former. 



ment of these small cells. While I have no 

 doubt that the interstices left between the 

 large cells and this central tube of epithelium 

 are also filled up by numbers of cytoblasts, of 

 excessive delicacy, and various degrees of mi- 

 nuteness ((/, B and c). 



Besides these free cytoblasts within the tube, 

 we may find others of endogenous origin. Very 

 careful observation of the large oval cells will 

 show that they enclose cytoblasts in addition 

 to their minutely granular contents (compare 6, 

 Jig. 246.). The number of these cytoblasts ap- 

 pears to vary from two to twenty in different 

 cells. They are excessively delicate, of about 

 1 nnrvth inch diameter: their shape is a flat- 

 tened oval ; and they contain a bright spot or 

 nucleus. They seem to be chiefly in contact 

 with the inner surface of the mother-cell ; so 

 that in many animals, specimens of their out- 

 line can often be distinctly seen through the 

 nearly transparent wall of this cell under the 

 higher powers of the microscope. They may, 

 however, be easily overlooked. And their 

 distinctness never equals that of the proper 

 nucleus of the cell ; closely as they resemble 

 this structure in size and shape. They may 

 sometimes be seen projecting from the broken 

 half of a mother-cell ; or set free from it, 

 owing to its having been ruptured by the 



Y 2 



