FOOD HABITS (S.S.433)j3i 



of both the mononch and the monhystera, without the body wall of either 

 nema being very plainly visible : it is somewhat as if one looked through 

 the walls of two glass tubes, one within the other, to view comparatively 

 conspicuous objects in the inner tube. Such an observation might easily 

 lead to the conclusion that the mononch had been feeding upon unicellular 

 algse. The deception is heightened after the body of the monhystera is 

 partially digested, for then all vestiges of the monhystera become practi- 

 cally invisible, and there are left as comparatively conspicuous remains 

 the less readily digested vegetable matter, lying loose in the intestine of 

 the mononch, the frustules of diatoms for instance, which of course 

 are wholly indigestible. Taking everything into consideration, it is not 

 in the least surprising that hitherto observers have been deceived as to 

 the food habits of mononchs. 



As nematologists heretofore have not carefully studied the food habits 

 of mononchs, particular attention was given them in the course of these 

 investigations ; but in spite of the care exercised much remains to be dis- 

 covered. The mouth parts and digestive organs have come in for special 

 study, since it is mainly here that we get clues, faint and puzzling though 

 they be, that help interpret the little we can glimpse of the food habits of 

 these organisms in their natural state. Soil mononchs live in darkness 

 and, as might be expected, behave in a wholly unnatural way when placed 

 in water on a microscope slide and brought in a drowning condition 

 into the blaze of light necessary to a microscopic examination. The dif- 

 ficulties and delays attendant on such a line of research are manifest. 

 Nevertheless, certain fundamental facts have been established; new or- 

 gans have been discovered and light has been thrown on the true nature 

 and function of organs not hitherto understood. It has seemed best to 

 dwell on the various habits and functions while describing the structures 

 with which they are associated. 



As we gain familiarity with the food habits of nemas, it becomes pos- 

 sible on this new basis to make comparative anatomical studies, the results 

 of which may be applied in determining the food habits of newly discov- 

 ered genera and species. 



I 

 STRUCTURE, FUNCTIONS, AND DISTRIBUTION OF MONONCHS 



The mononchs constitute a genus of free-living, predatory nematodes 

 inhabiting soil and fresh water, as well as the above-ground parts of cer- 

 tain plants. The average form and size of a mononch is indicated by the 



2.2 7.4 25. '63 >2S 92.7 



following average formula: 2 - 4 mm -* 



2.1 2.6 3. 3.2 2. 



* This formula, which is now coming into more general use, is simply a decimal method of 

 stating concisely the necessary measurements. The formula is fully explained in the appendix, 



r. 184. 





