44 



Appendices to Second Annual Report 



There is no distinct muscularis mucosa?. The submucous coat is well 

 marked, and presents the ordinary structure. The muscular coat consists 

 of a thin external longitudinal layer of non-striped muscular fibres, and a 

 much thicker internal circular layer. 



The lower narrow tubular part of the gastric sac or crop contains glands 

 with very short secretory tubes. Two folds of mucous membrane, on 

 opposite sides of the tube, are continued into it. These two folds seem 

 to pursue a somewhat spiral course, and meet in the middle line, so as to 

 divide the continuation of the tubular portion into two compartments. 



Pneumatic Duct. 



The pneumatic duct is the continuation of the tubular end of the gastric sac 

 or crop, and opens into the air-bladder about its middle. Viewed from the 

 outside, the spiral fold of mucous membrane, dividing it wholly or in part 

 into two, can be seen. All the coats of the crop are represented in this tube, 

 but the glands have disappeared. PI. II. fig. 5, shows it in transverse section. 

 Externally, c represents the longitudinal muscular fibres, m the circular. 

 The folds have met in the middle line, so as to divide the tube into two 

 compartments; and it will be observed that the muscular tissue takes 

 part in the formation of the septum. Each half of the tube is lined by 

 mucous membrane, covered by a single layer of columnar epithelium 

 resembling that lining the crop. At first sight it appears as if one had 

 to do with a series of branched glands, but the appearance shown in 

 fig. 5 is due to a series of fine complex longitudinal folds in the mucous 

 membrane. Sections of nerves and blood-vessels are seen on opposite 

 sides, near the outer part, while at one side (x) the mesentery is attached. 

 A large number of worms coiled up, so as to form circles, are often 

 attached to the outer surface of the pneumatic duct. 



There is a very striking difference, and at the same time a resemblance, 

 between the glands of the crop of the herring's stomach and the 'glands 

 ' of the fundus,' or those glands that lie in the cardiac and middle portions 

 of the mammalian stomach. What strikes an observer is the remark- 

 able resemblance between the cells lining the secretory portions of 

 the gland tubes and the ' outer ' cells in the mammalian stomach. The 

 point of difference is that these tubes are lined by a single continuous 

 layer of these cells. I, like Edinger, have been unable to find any 

 layer of cells lying internal to them comparable to the 'inner' cells 

 of mammals. Thus, these glands are simpler than those in mammals, 

 and this perhaps is just what we might have expected. There is not 

 yet that differentiation of tissue which is brought about by specialisa- 

 tion of function. Suppose the epithelial cells lining the crypts or ducts 

 are concerned in the secretion of mucus, then it is evident that in the 

 stomach of the herring (and in nearly all other fishes) the pepsin and the 

 hydrochloric acid of the gastric juice must be formed within in the same 

 cells, unless one supposes that certain of these cells secrete the hydro- 

 chloric acid and others the pepsin. This is very unlikely, so that one 

 cell may subserve two functions, nor is there anything against this view. 

 Looked at from the point of view of the evolutionist, one might say 

 as yet these two functions — the secretion of an acid and the formation of 

 a ferment — have not as yet in fishes been relegated to two distinct kinds 

 of cells, as happens in the mammal's stomach, where one set of cells 

 secretes the acid and another set the pepsin. One has only to recall to 

 mind the liver cells to understand how one cell may perform several 

 functions. Thus the liver cells not only secrete the bile, which in itself 

 is an extremely complex fluid chemically, but these same cells form gly- 

 cogen, and contain a ferment which transforms glycogen into starch. 



