They become very large and closely packed immediately beyond the common entrance of the biliary and pancreatic ducts and continue to be well developed and numerous throughout the rest of the duodenum and upper half of the jejunum (Figs. 308 and 309). From here on they become smaller, more irregular and less closely packed, and finally in the terminal two feet of the ileum disappear almost entirely (Fig. 309). This varying development of the valvulae is the chief reason why a given segment of the ileum weighs less than a corresponding length of the jejunum. This reduction in the fold-formation of the intestinal mucosa toward the terminal portion of the midgut is seen even in the lower vertebrates. Thus in Fig. 112, showing the entire intestinal tract of the conger eel, _Echelus conger_, in section, the plicae of the mucous membrane in the proximal segment of the midgut, at and immediately beyond the entrance of the biliary duct, are prominent and numerous. This redundancy continues but slightly reduced in the descending limb of the intestinal loop, while in the ascending limb and up to the ileo-colic junction the folds are reduced to a fine reticulated meshwork. Beyond the ileo-colic valve plate, in the short endgut, the mucosa again presents numerous pointed reduplications. II. ENDGUT OR LARGE INTESTINE. In this segment of the intestinal canal the undigested remnants of the food are collected and evacuated from time to time. In addition, the mucous membrane of the large intestine absorbs all _digested_ material which is passed from the small intestine. While digestion of food-substances will not be _inaugurated_ in the large intestine, material already in the process of digestion and mixed with the intestinal juices of the preceding segment, will be further elaborated in this portion of the canal and the nutritive products absorbed. This is especially the case in herbivora and omnivora, whose food is bulky, containing a large amount of refuse material, and is hence only slowly digested. On the other hand the food of the carnivora is easily and rapidly digested and absorbed. After passing through the small intestine hardly any substances remain which are capable of digestion and absorption. Hence the large intestine of herbivora and omnivora is uniformly longer in proportion to the small intestine than it is in carnivorous animals. In the former this segment of the canal functions as an accessory digestive apparatus and hence, as we will see, often develops accessory structural modifications, such as a large caecum and spiral colon, while in the latter it acts almost solely as a canal for the evacuation of the indigestible remnants.