OF THE NEMATOIDS, PABASITIC AND FEEE. 603 



imagine, from the situations in which they are found, that the very existence of organs 

 destined to facilitate such a process of oxidation would only be productive of evil 

 rather than good. And the fiacts revealed by the anatomy of these animals tend to 

 support this a jpriori assumption. We meet with glandular structures and excretory 

 organs in abundance, but with no trace of a special apparatus destined to secure an 

 aeration of the tissues ; such a function is, I believe, almost in abeyance in the parasitic 

 Nematoids, whilst the glandular and eliminatory function is more than ordinarily deve- 

 loped. 



It seems absurd to imagine that the two longitudinal tubes, in connexion with the 

 ventral pore in certain species of the genus Ascaris, could be destined to admit external 

 fluids for the purpose of respiration. And even if all evidence were not opposed to this 

 suggestion, a consideration of the more rudimentaiy condition of this apparatus, as met 

 with in the genus Strongylus and so many other Nematoids, would of itself go far 

 towards its refutation. Here we have undoubtedly to deal with an excretory glandular 

 apparatus. No one could for a moment regard these structures as at all analogous to 

 vessels destined alternately to receive and discharge an external fluid medium. I 

 believe that in the Trematoda and Tceniada also, where similar, though often more 

 developed systems exist, their function is in like manner one of a purely eliminatory 

 kind, and I cannot therefore but look upon the name of " water-vascular" apparatus 

 as a singularly inappropriate appellation for this system of vessels. 



In those Nematoids in which this excretory system is most developed, where the 

 vessels or tubes composing it are lodged in the lateral bands or developments from 

 them, it may be, perhaps, that these cellular structures bear the relation to them of 

 parenchyma to gland-ducts. It may be noticed also, that in the Strongyli, Oxyurides, and 

 many free Nematoids in which this excretory apparatus exists in the more undeveloped 

 condition of a ventral gland, its eliminatory function appears to be supplemented by the 

 presence of almost similar glandular structures in connexion with the anus and vagina. 



With regard to the integumental pores, they seem also to countenance the belief that 

 the deep integumental layer is to a certain extent an excretory organ, and I am in- 

 clined to look upon them as a series of excretory channels in connexion with this struc- 

 ture, having a sort of distant analogy therefore with sudorific ducts. That such is their 

 nature is to a certain extent countenanced by the fact of their extreme abundance in the 

 Trichocephali and Trichosomata, in which no ventral gland or other modification of this 

 excretorj' apparatus is to be met with ; so that the function of these seems to be per- 

 formed by the cellular bands and related integumental pores so universally met with in 

 the animals of this group. Amongst the free Nematoids, too, the very species in which 

 these integumental channels are met with in the most marked abundance, such as Dory- 

 laimus stagnalis and Lepfosomatum figuratum, are also those in which there is to be 

 found no trace either of ventral, anal, or vaginal glands. 



Amongst the free Nematoids we might expect to meet with some evidence of the per- 

 formance of the aerating portion of the respiratory process, and I think this may be 



4o2 



