434 y. A, I'oTTS. 



or ill earth saturated witli such substances" ; and (3) A iiguil- 

 lulida3, the rest of the free-living" nematodes, found in soil 

 or water. Such a classification, grounded on oecology, pays 

 no attention to tlie facts of morphology, and is naturally out 

 of phice in zoological arrangement, which aims at expressing 

 the relationship of animals by descent. The metliods of life 

 of ail jitiiiiial are, moreovei", largely ruled by the mode of 

 procuring iiutrimeiit which has been adopted. The first two 

 groups of Orley are parasites and saprophytes respectively, 

 but in the A nguil lul ida3 we have a heterogeneous collec- 

 tion of forms varying greatly in their habits of life. Little 

 is known of their sources of nourishment save in the case of 

 a very definite division (e.g. Ty lench u s, Doi-y 1 ai mus), 

 Avhich live on the juices of ])l:iiits, and for that end are 

 provided with a small protriisible spear for piercing tissues 

 and suctorial pharynx for absorbing sap thus set free. The 

 vast majority of this family, however, possess an unarmed 

 buccal cavity ; but in all the muscular pharynx i.s constantly 

 at work, now dilated, now collapsed, constantly pumping 

 flnid through the alimentary canal. There is no morpho- 

 logical (distinction to be observed between such a free-livinjr 

 nematode as is found in the mud of a lake or amongst the 

 algte of the marine littoral and a Rhabditisor Diplogaster 

 of the soil. But the latter class can be keot in a culture 



1. 



fluid which swarms with bacteria, in which individuals of 

 the former class would speedily succumb. The tissues of a 

 Rhabditis must be resistant to bacterial action and unharmed 

 by the toxins which such organisms produce, and the worm 

 is, in fact, capable of building up protoplasm from the 

 bacteria themselves or from the products of their action. 

 These are the most prominent physiological characteristics of 

 the soil nematodes, Orley's RhabditiforniEe, and account 

 for the peculiai'ities of their distribution, for they are 

 apparently absent from dry soils and those Avith a small 

 admixture of organic matter, and even in soils rich in humus 

 are only detected in quantity b\^ allowing some animal or 

 vegetable substance to putrefy on the sample. Sufficient 



