OF THE NEMATOIDS, PAEASITIC AND FBEE. 553 



Papillae agreeing in all respects with those described above, save that the external 

 aperture is oftener in the centre of a slightly concave depression rather than of a convex 

 eminence, are met with in single or double series in the ventral region, above the ano- 

 genital aperture of male Ascarides. In A. lumbricoides, on the posterior part of the 

 body, for a length of 1 J" there are about forty of these papilla; on each side of the ventral 

 region (Plate XXII. fig. 20). The anterior ones, gradually diverging more to the 

 lateral aspect of the body, are in single file and about ^" apart, but posteriorly they are 

 closer together and the linear arrangement is not preserved. These papillae may be 

 well seen in transverse sections (Plate XXIII. figs. 3 & 4, ^, I). I have seen well-marked 

 suctorial papillae also in the males of Heterakis acuminata (Plate XXII. fig. 13) and 

 Oxyuris vermicularis ; and besides bodies of this nature, in Cucullanus heterochrous there 

 is also a very large and prominent sucker-like body in the mid-ventral region. In the 

 same situation, a large and peculiar body of a similar nature is found in Heterakis vest- 

 cularis*. In short, structures of this nature seem much more commonly present than 

 absent in the males of parasitic Nematoids, whilst in the free species the reverse condi- 

 tion appears to obtain. Such bodies are, nevertheless, well developed in the genus 

 Leptosomatumf, whilst a series of integumental channels variable in number exist in the 

 same region of most Dorylaimi. The bodies which I have called " supplemental organs " 

 existing in the males of the genera Enoplus, Phanoderma, and Anticoma, seem altogether 

 problematical in their nature:};. 



In the free Nematoids we meet with an organ fully in harmony with the require- 

 ments of these animals, but which, from their different mode of life, neither exists nor 

 is needed in the parasitic species. I allude to the terminal tail-sucker which is found 

 in both sexes in nearly all the marine species, and in those of about half the land and 

 freshwater genera. It is the only kind of organ of prehension with which these minute 

 animals are provided, and is rendered all the more necessary by the smooth and polished 

 nature of their integuments. It is most constant, too, and best developed just in tliose 

 species which require it most — in those living amongst the sand and stones of the sea- 

 shore, in its surface-mud, or tenanting the fine weeds in its rock pools, which day by 

 day are exposed to the ever-moving currents raised by wind and tide, and which would be 

 continually swept from their natural haunts were they not provided with some means 

 of attaching themselves to surrounding objects. In its simplest form, such as we find 

 it in the members of the freshwater genus Mononchus, all we can recognize is a very 

 slight roundness and increase of size in the narrow terminal extremity, with a central 

 aperture ; but where it is more developed, as in the genus Enopltis, or Leptosomatum, 

 in addition to the terminal extremity being slightly swollen, we see the terminal aper- 

 ture continued inwards as a canal, and terminating after a short distance at a more solid 

 though perforated portion, to which are attached three pyriform sacs or elongated 

 tubes §. In the genus Enoplm these sacs occupy the cavity of the body posterior to the 



* Wiirzb. Naturwiss. Zeitsch. Erst. Bd. 1860, Taf. ii. 2 (Eberih). 



t Trans, of Linn. Soc. vol. xxv. pi. 12, fig. 163. + See figures, he. cit. § See figures, loc. cit. 



MDCCCLXVI. 4 H 



