Dr. L. Orley on Nematodes. 307 



rating them from the Rliahditiformre, at least until more 

 exact study shall show other limits to be necessary for the 

 group. 



Now the Ehabditiforniffi lack all the chief points usually 

 coincident with a free life — namely, the circumoral bristles, 

 lateral circular markings, and caudal sucker. Those struc- 

 tures which have been pointed out in some Rhabditidffi as 

 short bristles around the mouth are rather to be described 

 as long pointed papillte, and occur in some other parasitic 

 forms as well. Almost all Rhabditidaj possess an oesophagus 

 with either two roundish swellings or one elongated anterior 

 dilatation, and with a terminal bulb provided with a val- 

 vular apparatus. An oesophagus of this kind is found else- 

 where only in the genera most nearly akin to them {Plecfas, 

 Diplogaster)^ and iu the representatives of the genus Tijlen- 

 chus (the parasite of plants) — a proof that the passage to a 

 parasitic mode of life is marked by a modification of tliis kind 

 in the structure of the oesophagus. The TijlencM^ however, 

 in their other characters are very nearly related to the Rhab- 

 ditiform^e, inasmuch as the above-mentioned characters are 

 wanting in them ; and I hope the time may come when a 

 closer examination will allow us to place them with the lihab- 

 ditiformai as a distinct genus. 



Summing uj) what has been said, we find that there are 

 perhaps few orders in which so continuous a series of forms 

 exists as in the Nematodes. But that it is possible to separate 

 by a transitional group the two divisions distinguished by 

 Bastian I have now endeavoured to show ; and even if I have 

 carried out this separation imperfectly, I should still have for 

 consolation the expectation that the careful researches of 

 Leuckart, Claus, Blitschli, and De Man will yet enable us to 

 establish more satisftxctory boundary lines. 



Although the complete chain of forms is not known to us, 

 and although our present knowledge allows us only tenta- 

 tively to fix boundaries to the groups, I take the liberty of 

 proposing the following three suborders as tliose which best 

 represent our knowledge up to the present time. 



I. Xematentozoa. — Thread-worms completing their early 

 stage in the free condition, their maturity as parasites in the 

 bodies of the higher or the lower animals ; the species being- 

 perpetuated by the production of immense numbers of ova, 

 Avhose develo])ment is more or less complicated. The cuticle 

 is fairly thick, the mouth provided with papillas and lips ; the 

 buccal cavity and the male caudal end may be either simple 

 or complex. Tlie nervous system consists of distinct nerve- 

 cells and fibres, surrounds tlic oesophagus, and is always well 



