1902.] NATURAL SCIENCES OF PHILADELPHIA. 285 



light oil these aiid kindred problems, the present study was under- 

 taken at the suorgestiou of Prof. E. G. Conklin, in the Zoological 



't-b 



Laboratory of the University of Pennsylvania. 



It is a pleasure to expi-ess at the outset my gratitude to Prof. 

 Conklin, both for turning over to me a subject on which he had 

 made many observations and for rendering great assistance by 

 suggestion and direction throughout the course of the work. 



II. Material and Methods. 



Several features combine to make the digestive organs of the land 

 isopods especially favorable for a study of this kind. The digestive 

 glands are simple tubes made up of a single-layered epithelium, 

 which is bathed by the coelomic fluid. I'rom this the cells derive 

 directly the substances elaborated into the ferments; and the secretion 

 discharged at their luminal surface is poured into the anterior end 

 of the intestine, where it is mixed with the food, partially at least, 

 as it enters. That portion of the intestine which performs an ab- 

 sorptive function likewise possesses a single-layered epithelium 

 composed of very large cells. Without going into details here, it 

 is enough to say that the size of the cells is equaled, sof ar as is 

 known to the writer, by those of a similar absorbing organ of only 

 one other animal, the larva of Ptychoptera contaminata (2). In a 

 word, the plan of organization which is shared by the digestive sys- 

 tem of all Arthropoda, has here been carried out with diagram- 

 matic simplicity. 



Whether we regard the organization of the intestine as an adap- 

 tation to the mode of life or the feeding habits as an adaptation to 

 the organization, there is plainly a very nice relation between the 

 two. Microscopical examination of the intestinal contents shows 

 that in proportion to the quantity of digestible matter a very large 

 part is wholly indigestible. Bits of dead leaves, wood fibres and 

 various other masses of thick-walled vegetable cells, some clearer, tliiu- 

 walled cells, which I take for hyphal cells of fungi, are among the most 

 commonly observed substances.'* In addition there are in the intes- 

 tine numei'ous crystalline Iwdies, doubtless of an inorganic nature, 

 the skeletal remains of insects, and micro-organisms. But the 



* I have frequently seea pill-bugs eating edible mushrooms and have 

 observed that they shun poisonous species. 



