344 Dr. T. Williams on tlie Mechanism of Aquatic 



Annelids. From the latter, however, they differ in one extraor- 

 dinaiy particular. The Nemertinidse, Planariae and Clepsinidae 

 excepted, in all Annelids the chylaqueous fluid is corpusculated, 

 and the blood-proper is entirely destitute of all morphous par- 

 ticles. In the Nematoid Entozoa these conditions are reversed. 



In the Cestoid and Trematoid genera the fluid contained in the 

 digestive diverticula, through its floating cells, enacts that office, 

 which, in the example of the Nematoid worms, is transferred to 

 the blood-proper, and in that of the Annelids in general to the 

 chylaqueous fluid. This circumstance, however, does not imply 

 that in the Nematoidea the blood-proper system is preponde- 

 rantly developed. It consists only of two principal longitudinal 

 trunks, adherent at the ventral and dorsal median lines to the 

 internal surface of the integumentary cylinder. Cloquet has 

 described the blood-system in several species. Ecker* has also 

 defined a blood-system in a species of Filaria. The \Aoodi-vessels 

 of the Nematoid worms exhibit a distinct red colour. It is not 

 yet certain that the contained blood partakes of the same colour f. 

 Rudolphi has characterized these and all Entozoa as white- 

 blooded worms. The primary trunks are connected together by 

 means of transverse secondary branches : these latter can only 

 be discovered in the substance of the integuments, not on or in 

 the parietes of the viscera. The blood-proper of the Nematoid 

 worms is indeed a very subordinate constituent of the organism, 

 quite insufficient to supply the solids with the materials of in- 

 crease, and not less unequal to the function of breathing. A 

 few blood-vessels distributed scantily over the cutaneous surface 

 would pi'esent too limited a surface of contact with the sur- 

 rounding element to receive a proportion of oxygen adequate to 

 siipply the wants of an organism so large as that of Strongylus 

 Gigas. By inference it becomes obvious that some other fluid 

 element of nutrition in these genera is required to minister to 

 the exigences of the solid parts. It is accordingly found that in 

 the Nematoid orders the chylaqueous fluid is relatively abundant 

 in quantity : this fluid is contained, as in the cylindriform An- 

 nelids, in the peri-intestinal or visceral cavity (figs. 10, c ; 

 11, d; 12, c). In the round worms this cavity occurs under 

 two distinct anatomical conditions. In one case, illustrated 

 in the example of Ascaris Lumhricoides (fig. 11), the intestine 

 is tied by frequent transverse bridles to the integumentary 

 cylinder : these bridles intersect the cavity, and limit the 

 motion of the contained fluid. They stretch outwards through 



* Miiller's Archiv, Ueber ein Gefassystem in eingepuppten Filarien, 

 S. 606. t. 15. figs. 3, 4, 1845. 



t For a further statement of the author's researches on this subject, see 

 his papers in the ' British and For. Med. Chirur. Rev.' 



