286 PROCEEDINGS OF THE ACADEMY OF [May, 



scanty pi'oteid content of such food is compensated for by the very 

 efficient absorbing surface. 



Judged by the number of pellets of waste, the quantity of food 

 eaten seems prodigious. An animal kept in a clean dish on a 

 piece of moist bark will cast from twenty to fifty in twenty-four 

 hours. The number is about the same for all the species. Brought 

 fresh from the natural state and deprived of food the number cast 

 in a single night (about fifteen hours) averages, for a large number 

 of counts, between five and six ; in the next twenly-four hours the 

 average number decreases to three. (This decrease is explained by 

 the fact that only the anterior half of the " mid-gut" is provided 

 with strong musculature. In the absence of muscles strong enough 

 to empty the posterior portion, and with no fresh food to crowd 

 back the remainder, its progress is very much slower ; some of it, 

 indeed, may lodge just anterior to the sphincter for as long as two 

 or three weeks, where it may be recognized as a little black mass in 

 the region under the first abdominal segments. ) The anterior por- 

 tion is emptied, as can be seen by holding the animal up to the 

 light, during the first night. Since then five or six pellets repre- 

 sent the contents of the anterior half of the " mid-gut," the animal 

 must eat, in the course of twenty-four hours, an amount which fills 

 the intestine from two to four times. 



The several indigenous species of terrestrial isopods are equally 

 favorable. Those which I have used are Porcellio spinieornis, 

 Porcellio scaber, Onisciis asellm, Philoscia vittata and Cilisticus 

 convexm. 



A reserve stock of animals, renewed from time to time, has been 

 kept in the University Vivarium surrounded by the natural objects 

 among which they were found — bits of bark, dead leaves, etc. 

 Placed in large glass evaporating dishes, covered with a glass plate, 

 on the under side of which was kept moist filter-paper for preserving 

 the proper humidity of the atmosphere, the animals behaved in 

 eveiy respect as in the natural state. In the feeding experiments, 

 to be described later, it was necessary first to empty the intestine of 

 all food. The method commonly employed for this was merely to 

 isolate animals in dishes covered as above described and cleaned 

 once or twice daily. No difficulty was experienced in keeping the 

 animals alive in this way so long as starvation was not Moo pro- 

 longed, provided only the atmosphere was kept moist by daily 



