OF THE NEMATOIDS, PAEASITIC AND FEEE. 



685 



ventral region has been rather a stumbling block to anatomists on account of the different 

 bodies with which it was connected ; in some cases it appeared as the exit of a system 

 of tubes, whilst in others it was connected with glandular bodies of different sizes, 

 sometimes single and sometimes double; and lastly, Walter* almost certainly alluded 

 to the same opening when he spoke of an anterior ventral sucker existing in the young 

 of many Nematoids, which he believed either to retrograde or entirely disappear in 

 the adult animals. There can be little doubt, however, that we may dismiss this state- 

 ment of Walter's at once as being altogether erroneous. And if it be carefully borne 

 in mind that no observer hitherto has ever discovered more than a single aperture in 

 this situation, I think I shall be able to simplify the whole subject, and also be able to 

 advance cogent reasons for the belief that all the various bodies hitherto met with in 

 connexion with this ventral aperture, are only modifications in the development of one 

 common system answering to the so-called " water-vascular system," so well known to 

 exist in the Trematoda and other animals. 



The most elementary structures met with in connexion with the ventral opening have 

 been figured and described by Dr. LEiDYf in a species oi Hystrignathus, andbyEsERTHj 

 in Ascaris oxyura and Oxyuris amhigua, in which minute saccules are met with, exhi- 

 biting a very rudimentary condition of the so-called "ventral gland." Amongst the 

 free Nematoids, in Cyatholaimus ornatus (Plate XXVIII. fig. 36), Sphcerolaimus hirmtm, 

 the members of the genus Enoplus and others, we find it slightly more developed, inas- 

 much as it exists as a tubular organ extending from the ventral aperture near the middle 

 of the (Esophagus, to or nearly as far as the termination of that organ. It has granular 

 contents, and its calibre is uniform except at its blind extremity, where it is very slightly 

 enlarged. In Linhomoeus hirsutum and L. elongatum it is a little longer, extending as 

 far as the commencement of the intestine, which is compressed by the more developed 

 condition of its blind termination. This appears of a dilated pear-shaped form, and is 

 filled with granular contents, in which is imbedded a clear, solid, homogeneous looking 

 body or nucleus §. This or the former represents the condition of the ventral gland in 

 most species of the marine Nematoids, and it seems present in almost all the genera. In 

 the land and freshwater species, however, I have recognized a ventral aperture and gland 

 only in the members of four genera, Aphelenchus, Cephalolus, Tylenchus and Plectus, and 

 in these it is somewhat modified in form. The duct, instead of being a wide membra- 

 nous tube, is here a narrow and rather rigid structure, extending with a gentle curve 

 towards the centre of the body, as may be best seen with adult specimens of Tylenchiis 

 tritici (Plate XXVIII. fig. 17), or having altogether a twisted duection, being two or 

 three times bent upon itself, as occm-s in the various species of the genus Plectus (Plate 

 XXVIII. fig. 14.). It is extremely difficult to ascertain the precise mode of termina- 

 tion of this duct, but after the most prolonged examinations I am enabled to assert 

 pretty confidently that in Tylenchus Davainii this tube communicates with a rather small 



* Vide KDchenmbistee (8yd. Soc. Transl.), p. 365 and note. t Smithson. Contrib. 1853. 



t TJntereuch. Uber Nemat. Taf. viii. 9, 10. § Vide figures, Trans, of Linn. Soc. vol. xxv. 



MDCCCLXVI. 4 M 



