Respiration in Invertebrate Animals. 345 



the whole thickness of the integument under the character 

 of transverse muscular fasciculi. They are accompanied by 

 open passages by which the chylaqueous fluid reaches the 

 cutaneous surface for the purposes of aeration. The longitudinal 

 muscular bands, with their embracing spaces, establish between 

 the transverse, free communications. It is thus clear, that 

 although the integuments in certain species of Nematoid worms 

 are remarkably dense and resisting, they are permeated by chyl- 

 aqueous fluid to an extent enough to subserve the purposes of 

 breathing. The intimate connexion which in some Nematoid 

 worms subsists between the intestine and integument, limits the 

 movements of the intestine. It is to this anatomical circum- 

 stance that the motionless state of the chylaqueous fluid in these 

 worms is to be ascribed. In consequence of the absence from this 

 fluid of all visible globules, to detect its existence is not easy 

 to the uninitiated observer. 



It is upon the freedom with which the intestinal cylinder 

 moves within the concentric integumentary, in many species of 

 Annelida, that the rapid and unobstructed oscillations of the 

 interposed chylaqueous fluid depends. ^^Tiy should the same 

 fluid, occupying the same locality, be required to move so little 

 in the Entozoa ? The answer probably is, that in the two indi- 

 cated instances the fluid difi'ers materiallyin chemical composition. 

 The second type (fig. 10) of Nematoid Entozoa is exemplified 

 best in the case of the large Strongylus, constantly to be found 

 in the small intestine of the sheep. Here the intestine, a straight 

 tube, is considerably smaller in diameter than the space included 

 by the integuments, while it is tied at few points to the latter. 

 The visceral chamber is therefore unusually capacious in dimen- 

 sions, and the enclosed fluid is considerable in bulk. It is a 

 fact of unusual interest, that the chylaqueous fluid, whether sta- 

 tionary or moveable in its containing chamber, of all Nematoid 

 Entozoa, is perfectly homogeneous and destitute of every trace 

 of visible element. In these worms the digestive system does 

 not lodge a corpusculated liquid, of which the suspended cells 

 supersede the necessity for the agency of similar cells in the 

 extra-intestinal chylaqueous fluid. It must therefore be infen-ed, 

 that the true blood of these worms is the seat of the floating cell 

 agency. If it should be hereafter proved by exact observations, 

 that neither the true blood, nor the chylaqueous fluid, nor the 

 intra-intestinal chyme is charged with floating cells, these ani- 

 mals will constitute an exception unique in the animal kingdom, 

 in which an animal organism is sustained without a single 

 corpusculated nutritive fluid. 



The principle is at present inadmissible in science, which sup- 

 Ann. i)- Mag. N. Hist. Ser. 2. Vol. xii. 24 



