DIGESTIVE SYSTEM OF PERIODICAL CICADA. 2OQ 



periods of feeding and growth. Experiments show that for the 

 salmon it may be five to eight years; for the ephemerids two or 

 three years; while for the cicada thirteen and seventeen years. 

 In these groups this long period is now believed to be generally 

 concerned in accumulating reserve potential energy, most of 

 which will sustain an important relation to the brief, but crucial 

 period of activity and perfecting the reproductive elements, and 

 their union for the preservation of the species. 



2. In each of these groups this actively cumulative growth 

 and storage of energy, followed by a relatively brief period of 

 reproductivity, gives that anomalous reaction of decline and 

 death a unique significance. 



3. Corresponding to these extended and painstaking researches 

 of Greene I know of nothing among insects or other inverte- 

 brates; but the remarkably analogous aspects of the cases lead 

 me to conclude that the physiologic activities involved in the 

 latter are more or less similar; in some respects identical, with 

 the former. 



THE POSTERIOR CROP. 



Under this caption, the junior author in his earlier paper has 

 described a most unique and anomalous organ, clearly, as I 

 believe, a part of the digestive system. For a full account of its 

 anatomy reference may be made to his description in the paper 

 just cited. It must suffice here to briefly summarize its main 

 features. During nymphal life, as is well described in the second 

 section of this contribution, it is rather small, "with walls of 

 uniform texture and much folded. But in the adult, the walls 

 of the organ are distinctly variable in thickness. The outer 

 surface of the organ is closely apposed on all sides by fat. This 

 probably has something to do with the collapsed condition of the 

 tube in this region." A recent popular paper by Snodgrass 

 descriptive of this insect designates this organ on the contrary 

 as a part of the respiratory system. But, as will be shown later, 

 this seems decidedly erroneous. In my earlier account (Proc. 

 Onon. Acad. Sci., 1903, p. 51) I conceived it in adult life to act 

 in some way as an organ for aiding in the absorption of fat, its 

 epithelium in many cases being more or less charged with globules 

 of fat. This was confirmed by the work of Henderson who also 



