598 DE. H. CHARLTON BASTIAN ON THE ANATOMY AND PHYSIOLOGY 



closely to resemble that of a Strongylus ; but at a more advanced stage a specialization 

 occurs, the extremities of the gland no longer proceed with their development in the 

 general cavity of the body, but each tending towards that of its own side, perforates the 

 lateral band and continues to extend lengthways in its substance in the form of a uniform 

 tube or vessel. In the Ascarides the ventral aperture is situated far forwards towards 

 the head, whilst in other Nematoids, such as Cuciillanus heterochrous* , it is found 

 situated much more posteriorly, opposite the termination of the oesophagus ; and here, 

 accordingly, in addition to the two posterior branches which perforate the lateral bands 

 as in A. lumbricmdes, a still further specialization exists, and two anterior branches 

 are given off to occupy those portions of the bands in front of the median aperture. 



In that form of the so-called Filaria piscium which I examined, may be seen the rudi- 

 mentary condition of a more complex arrangement existing in Ascaris osculata and 

 A. sjjiculigera. Here a single tube in communication with the ventral pore leaves the 

 cavity of the body to perforate the left lateral band, in the axis of which it exists as a 

 simple unbranched vessel, whilst in A. osculata and A. spiculigera a corresponding tube, 

 also on the left side, sends off an infinity of inosculating branches which ramify in the 

 substance of the lateral band, and of a special development from it. The tubes in some 

 of these animals have positively been ascertained to be contractile in their nature, and 

 they seem generally to contain a clear colourless fluid with a variable number of small 

 molecules suspended in it. In A. lumbricoides the contained fluid is frequently of a 

 reddish colour. Although the body of the ventral glands is generally quite filled with 

 granular matter, still in the terminal portions of their duct I have frequently seen 

 amongst the free Nematoids a clear fluid with suspended molecules. I have especially 

 noticed this in Symplocostoma longicolle. 



I am fully impressed with the homological identity of these modifications of an excre- 

 tory organ, as met with in the Nematoids, with that system of vessels in the Trematoda 

 and other animals, which, from its invariable communication with the exterior, has been 

 termed a " water-vascular " apparatus. As I shall have again to allude to this subject 

 when treating of the affinities of the Nematoids, I will now merely call attention to the 

 following facts : — that in both Nematoids and Trematodes the nature of the contents in 

 this system of canals is the same, whilst in Distomum tereticollef, as in A. lumbricoides, 

 the fluid has been seen of an exceptionally reddish colour ; that in some species of Tre- 

 matodes, such as Monostomumfaba, Distomum cirrigerum, and Gasterostomumfimbriatum, 

 there exists in connexion with the external aperture only a simple sac ; in others, such 

 as Distomum chilostomum, D. clamgerum, D. conjunctum, D. luna, &c., as well as in several 

 species of the genus Monostomum, it is a bifurcated organ ; whilst in Amphistomum 

 conicum% four main branches exist, although each of these sends off an infinity of 

 offshoots. 



I have still to speak of two varieties of vessels met with in the Nematoids, which 



* Dacnitis esuriens of Dttjardin. t Siebold's Man. d'Anat. Comp. p. 137, note. 



t Cobbold's ' Entozoa,' plate 3. 



