XIV PREFACE. 



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

 are two openings at its anterior part by which it communicates 

 with the vibratile infimdibulum 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 capsulogenes, but they are found at the 

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

 ring on each side. 



In Tuhifex rwulorum and Nais ^^rohoscidea also the female 

 organs more or less invaginate the male. 



See D'Udekem Hist. nat. du Tuhifex des ruisseaux, Mem. couronne, 

 Acad. Roy. de Belgique, xxvi. 1855, by the same, Developpement duLomhric 

 terrestre, ibid, xxvii. 1S56. 



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 articidata., when 

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

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

 of the peritoneal cavity that the blood derives nutrient matter. 



See on this subject : Quateefages Mem. sior la caviti ginerale du corps 

 des invertebres, Ann. des Sc. nat., Ser. iii. Tom. xiv. pp. 302 — 320; Whar- 

 ton Jones, The blood-corpuscle considered in its different phases of develop- 

 ment, Mem. II. Invertebrates, in Phil. Trans. 1846, pp. 89 — loi ; Williams 

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

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

 system in Litmhricus, Hirudo and Nais, for which see also, Rymer Jones 

 Animal Ivinr/d. 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, xvii. 



In the class of insects Prof. Van der Hoeven is of opinion that 

 the order Strepsijjtera pp. 305 — 307 might conveniently be sup- 

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



