ON THE ANGUILLULIDE. 83 
detected, instead of these canals, two lateral, double-outlined, eolourless vessels, some- 
what similar to what I described in Dracunculus', 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- 
pletely {rom other structures”. These seem to correspond to the axial vessels contained 
within the lateral lines? of Ascaris lumbricoides, A. megalocephala, and other parasitic 
Nematoids. 
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) surrounding the cesophagus 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 peculiarities rather point to its affinity with 
the glandular than the nervous system (Pl. XI. fig. 126). The absence of any traces of 
nervous filaments in connexion with the well-developed ocelli of so many cf the marine 
species affords also strong negative evidence of the absence of such a system in the 
Nematoids. 
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. 3 
Much difference exists as to the muscular power and activity of different species, 
The Dorylaimi and Tylelenchi, for instance, are very slow and tardy in their movements ; 
Spherolaimus hirsutus is remarkable both for its activity and power ; whilst the different 
species of the genera Theristus and Tachyhodites 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 Nat- 
* Linn. Trans. vol. xxiv. p. 113, pl. 21. fig. 266. 
* Although not yet 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 only 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 
parasitic, and in nearly all the free species, in which the lateral lines can be detected, they appear to "e simple 
‘aggregations of large cells, bounded, internally at least, by a limiting membrane—though I think we may fairly look 
T these lateral lines of the free Nematoids as homologous with the lateral lines of the Ascarides, and consequently 
infer that they are also integral parts of a general subcutaneous cellular layer. In this cellular layer of 4. lumbricoides 
and 4. megalocephala Y 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, 
= fancy, open externally by means of minute pores through the integument, though hitherto I have been unable 
"horouglily to satisfy myself of the fact. d 
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 — i 
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