DIGESTIVE SYSTEM OF HYDROCORAX. 35 



membrane of the upper three-fourths has a velvet-like feel a.nd shows 

 long villi lying close together. At a point about 250 millimeters from 

 the rectum and about where one would expect to find the cfeca, if such 

 did exist, there is a short section of the gut which is dilated, has thin 

 walls, and an entirely different t^rpe of villi. This section is about 70 

 millimeters in length, and below it one again finds villi of the same 

 type as occur in the upper intestine. 



The intestine differs from the oesophagus in the position of the mus- 

 cular layers. A section shows externally the serous coat, made up of 

 connective tissue; next to this a well-developed longitudinal muscular 

 coat ; next, internal to this, the circular muscular layer. The muscularis 

 mucosffi lies internal to this circular layer and then comes the mucosa 

 with its epithelial lining. This is shown perfectly in the cross-section 

 of the gut where the outer longitudinal fibers are seen cut across and 

 the circular fibers are seen in their circular plane. Simple alveolar 

 glands lie at the base of the villi. 



After this brief description of the digestive tract, the following points 

 appear worth considering: I have collected three large hornbills at 

 practically the same time, months after the breeding season was over, and 

 fovmd the deciduous membrane in three different stages of development; 

 one was separated entirely from the stomach except for a narrow zone 

 around the cardiac opening, one was just beginning to form, and the 

 third was in an intermediate stage. At other seasons the same has been 

 found and in some, the sac, _ ready to be cast off, was packed full of 

 indigestible parts of the fruit on which the birds were feeding. It seems 

 reasonable to suppose that, at least when the breeding season is past, 

 the food, mixed with, and acted upon by, the secretion of the pro- 

 ventricular glands, passes into the deciduous sac lining the stomach ; here 

 muscular action completes the mixing, triturates the food, and prepares 

 the digestible parts to pass over into the duodenum. The refuse is then 

 periodically ejected in the membranous sac. Whether this routine is 

 changed at the breeding season, I can not say. 



Another point of interest is the abrupt change in the character of the 

 mucous membrane in the short section of the gnit at about the point one 

 would expect to find cseca; this, together with the dilitation and thinning 

 of the intestinal wall at this point may suggest the explanation of the 

 absence of caeca in certain species where the diet is similar to that of 

 others in which these organs are present. Is it not possible that the 

 mucous membrane of the gut itself talies on, in these specialized areas, 

 the functions performed by the c^ca in other birds? In Bubulcus for 

 example, where the bud-like, single c^cum is very short, the mucous 

 membrane of the adjacent gut contains numerous masses of lymphoid 

 tissue, from 90 to 250 millimeters in diameter, not found in other parts 



