XIV PREFACE. 



form of a vesicle and is completely invaginated in the ovary. There 

 are two openings at its anterior part by which it communicates 

 with the vibratile infundibulum on each side, which is the begin- 

 ning of the vas deferens ; after forming many convolutions each vas 

 deferens opens externally on the ventral surface of the 12th ring. 

 Here also are glandes capsulogdnes, but they are found at the 

 anterior part between the 5th and 8th rings, and open at the 5th 

 ring on each side. 



In Tubifex rivulorum and Nais proboscidea also the female 

 organs more or less invaginate the male. 



See D'UDEKEM Hist. not. du Tubifex des ruisseaux, Mem. couronne", 

 Acad. Roy. de Belgique, XXVI. 1855, by the same, De"veloppement duLombric 

 terrestre, ibid. xxvu. 1856. 



In this class the distinction between blood, generally red- 

 coloured and contained in close vessels, and the nutrient fluid of 

 the general cavity of the body (chylaqueous fluid WILLIAMS), 

 becomes marked. The blood contains no corpuscles, these are 

 confined to the fluid that circulates in the visceral cavity, which 

 is the product of digestion mixed with water. The form of the 

 corpuscles is various, is least constant in the lower classes, where 

 the chylaqueous is the sole nutrient fluid, but even in the molluscs 

 does not attain the regularity of form which prevails in the lower 

 vertebrates. These corpuscles in many of the articulate, when 

 removed from the body, send out processes like Amoeba, and are 

 supposed by N. LIEBERKUEHN to be parasites. It is from the fluid 

 of the peritoneal cavity that the blood derives nutrient matter. 



See on this subject : QUATEEFAGES Mini, sur la cavitt ge"ne"rale du corps 

 des inverte'bre's, Ann. des Sc. not., Ser. in. Tom. xiv. pp. 302 320; WHAR- 

 TON JONES, The blood-corpuscle considered in its different phases of develop- 

 ment, Mem. n. Invertebrates, in Phil. Trans. 1846, pp. 89 101 ; WILLIAMS 

 On the British Annelida in Report of Brit. Association for 1851, pp. 159 

 272, describing the blood-circulation and his views also of the generative 

 system in Lumbricus, Hirudo and Nais, for which see also, RYMEB JONES 

 Animal Kingd. edit. 2, pp. 272 275, pp. 282 284, pp. 287 289, and 

 WILLIAMS On the blood proper and chylaqueous fluids of invertebrate animals, 

 Phil. Trans. 1852, pp. 595 653; the same On the Mechanism of Aquatic 

 Respiration in Ann. and Mag. of Nat. Hist. 2nd Ser. Vols. xiv, xvi, xvn. 



In the class of insects Prof. VAN DER HOEVEN is of opinion that 

 the order Strepsiptera pp. 305 307 might conveniently be sup- 

 pressed. In all the genera included in it there appears to be the 



