LIFE HISTORY OF DESMOGXATHUS FUSCA. 28 1 



copepods in the stomach, and in the stomach of another specimen 

 of the same stage 6 copepods were found. 1 In all the cases which 

 I have examined, of aquatic larvae in which yolk was still present, 

 feeding has been extensive and fragments of partly digested 

 aquatic animals, in the main copepods and insect larvae, have 

 been found not only in the stomach but in various regions of the 

 intestinal tract. Whether the early assumption of its digestive 

 function on the part of the alimentary canal has the effect either 

 to retard the final consumption of yolk material through the 

 supply of nutriment from external sources, or to hasten its 

 consumption through the stimulation of the histogenesis of the 

 walls of the canal through use, I am at present unable to say. 

 At any rate the excess of the supply of yolk material over the 

 amount which the larva usually consumes before reaching the 

 water with its ample supply of appropriate food, is undoubtedly 

 an adaptation to a possible prolongation of the terrestrial period 

 such as might easily occur if the eggs happened to be laid at a 

 greater distance than usual from the water, or if an unusually dry 

 season during the period of development of the egg should 

 diminish the water supply in the brook and in the burrows 

 leading to it and thus lengthen the period which might elapse 

 before the larvae should reach the water. 



Internally the differentiation of the intestine from the mass of 

 yolk cells is a somewhat complicated process, the detailed 

 account* of which must be reserved for a more technical treatment 

 of the whole subject of the histogenesis of the alimentary canal. 

 Certain salient features of the process may, however, be discussed 

 here. 



At the time of hatching the duodenum is in what may be 

 termed the transition stage in its development (d, Fig. 12). 

 Anterior to the point where the bile duct leads into the duodenum 

 from the fully formed liver, yolk granules have disappeared, as 

 they have also from the cells of the liver and pancreas and their 

 ducts. Posterior to the opening of the bile duct into the duo- 

 denum, there is for some distance a well-defined lumen, but the 

 epithelial cells lining it contain a considerable number of yolk 



1 All of these individuals, though ranking as terrestrial larva 1 , happen to be 

 among the more precocious ones which had reached the water, where they had 

 access to food. 



