308 Dr. L. Oilej on Nematodes. 



developed. The genital tube is complicated by many convo- 

 lutions. 



II. Rhabditiformce. — Small, chiefly microscopic thread- 

 worms, which live generally free, but in exceptional cases as 

 parasites, and have without exception the power of deve- 

 loping to the sexually mature state in organic substances in a 

 state of decomposition, or in earth saturated with such sub- 

 stances, such condition being necessary to the process. Tlie 

 species is perpetuated not so much by the production of an im- 

 mense number of ova as by the habit which they have of living 

 in colonies, of developing with great rapidity, and with a meta- 

 morphosis which is either slight or complicated by dimorphism 

 of the sexes. They are devoid of all the principal cliaracters 

 usually coincident with a free life, such as circumoral bristles, 

 caudal suckers, and lateral circular markings. The cuticle is 

 tolerably tliin ; the nervous system consists more of tibres than 

 cells, and is feebly developed and often wholly wanting. The 

 oesophagus has two dilatations, the posterior of Avhich is 

 provided with a valvular apparatus. The genital tube is of 

 simple structure, not convoluted. The mouth has lips or 

 papilla3 ; the buccal cavity is usually very simple. 



III. Anguillulidie. — Small microscopic thread-worms lead- 

 ins; a free existence in mould' or in water throuii:hout all their 

 stages, developing without a complex metamorphosis. Though 

 small, they produce large eggs. Provided with the organs 

 belonging to a free life, such as bristles, caudal sucker, and 

 lateral circular markings, and even with eyes in many cases. 

 Buccal cavity simple or complex, according to the conditions 

 under which they live. The nervous system is either entirely 

 absent or composed only of a few tibres. Genital tube simple ; 

 no convolutions. 



The Nematodes of the British-Museum collection belons; to 

 the Nematentozoa, Avith the exception of two species which 

 belong to the group Khabditiformte ; the Anguillulidai are 

 not represented. With regard to the first group, I must dis- 

 tinctly lay down that not one of the existing classifications re- 

 presents the true relationships, and we shall certainly have long 

 to wait for a natural arrangement. Of all those wliich have 

 been proposed I have found that of Schneider to be the best ; 

 and although we have found the arrangement according to 

 the muscular system not to be thoroughly satisfactory, I have 

 adopted it provisionally. Fortius reason, this group includes 

 all the genera contained in Schneider's monograph, with the 

 exception oi. EnojAus^ Pelodera^ Lejdodera., AnguiUuhij Mermi'Sj 

 emd Gordius ] and it is divisible into the subordinate groups, 

 Polyinyarii, Meromyarii, and Ilolomyarii. 



