ON THE ANGUILLULIDiE. 83 



detected, instead of these canals, two lateral, double-outlined, colourless vessels, some- 

 what similar to what I described in Dracuncnlus \ and which are most apparent in 

 Tylelenchus tritici. In this species, from their being longer than the body, they are 

 wavy or even convoluted, and I have several times succeeded in isolating them com- 

 jiletely from other structures -. These seem to correspond to the axial vessels contained 

 within the lateral lines"' oi Ascaris lumhrlcoides, A. megalocephala, and other parasitic 

 Kematoids. 



I have met with no distinct traces of a nervous system in these animals, the only thing 

 which might be at all mistaken for a portion of such a system being the peculiar ring 

 (also observed by Eberth) suln-ounding the oesophagus in some of the marine genera'*, 

 concerning the nature of which we have both arrived, independently, at the same con- 

 clusion, that its connexions and structural j)eculiarities rather point to its affinity with 

 the glandular than the nervous system (PL XI. fig. 12G). The absence of any traces of 

 nervous filaments in connexion with the well-developed ocelli of so many cf the marine 

 species aff'ords also strong negative evidence of the absence of such a system in the 

 jN'ematoids. 



The muscles of the body seem to be, the same as in other Nematodes, composed of four 

 longitudinal bundles, two dorsal and two ventral, with an interspace on either side. " In 

 neither free nor parasitic have I been able to recognize the circular fibres spoken of by 

 some anatomists. 



Mucii difference exists as to the muscular power and activity of different species. 

 The Dorijlaimi and Tylelenchi, for instance, are very slow and tardy in their movements ; 

 Sphcerola'mms hirsntiis is remarkable both for its activity and power ; whilst the different 

 S23ecies of the genera Theristiis and TachyliocUtes are distinguished by rapidity of move- 

 ment. The mode of locomotion of all is indeed most characteristic, being effected by 

 eel-like undulations of the body, which at once distinguish these animals from the iVaiV 



' Liun. Traus. vol. xxiv. p. 113, pi. 21. fig. 26 i. 



- Although not )-et detected, I have little doubt that similar vessels will be found to exist in the fourth and nearly 

 allied genus Cephalobus. 



" Since this paper was read, I have ascertained that not onl3' the lateral lines, but also the mid ventral and dorsal 

 lines of the two Ascarides above mentioned are only local developments in these situations of a fibro-cellular layer 

 lining the whole internal surface of the chitinous integument, and separating it from the four great longitudinal 

 muscles. These developments (occupying the muscular interspaces) differ notably from one another, inasmuch as 

 those in the lateral regions, besides being much larger and more prominent than the dorsal and ventral cords, contain 

 each a well-marked axial vessel. Whether this vessel exists in all the Nematoids seems very doubtful, as in some of 

 the parasitic, and in nearly all the free species, in which the lateral lines can be detected, they appear to be simple 

 aggregations of large cells, bounded, internally at least, by a limiting membrane — though I think we may fairly look 

 upon these lateral lines of the free Nematoids as homologous with the lateral lines of the Jscarides, and consequently 

 infer that they are also integral parts of -a general subcutaneous cellular layer. In this cellular layer of ^. lumbricoides 

 and ,'/. megalocephala I have also detected a series of delicate transverse vessels, mostly in pairs, extending from the 

 mid dorsal to the mid ventral line, and much more numerous on the right than on the left side of the body. These, 

 I fancy, open externally by means of minute pores through the integument, though hitherto I have been unable 

 thoroughly to satisfy myself of the fact. 



■* As yet I have only met with it distinctly in some of the marine genera, and, curiously enough, in those species 

 only which have a plane or longitudinally striated integument, and never in those with transverse markings. 



m2 



