176 REPORT — 1851. 



part of the body it intimately penetrates. It is more probable, because more 

 in accordance with analogy, however, to suppose that it is a manufactory in 

 itself, that its corpuscles execute an office by which the mineral substances 

 and proximate principles are vitally assimilated, that the corpuscular elements 

 in the Annelida do in this fluid what in the higher animals analogous bodies 

 efl"ect in the blood-proper. From these facts the physiologist may advisedly 

 say thus much, that in these animals nature divides the vital fluids into two 

 separate and distinct orders, on one of which the preparative and elaborative 

 cell-agency devolves, on the other the work of solid nutrition. They prove 

 Avith great clearness that the corpuscular elements, either in the blood itself, 

 or as in this case, in some contributory fluid, are essential to the preparation 

 of the blood-proper ; for when in the zoological series, as in the higher 

 Articulata, this corpusculated fluid disappears, the blood itself becomes 

 corijusculated, or when the peritoneal fluid, as in the Echinodermata, 

 becomes less organic, then also morphotic elements are developed in the true 

 blood. From these observations the inference may be further drawn, that 

 between these two nutritions fluids there exists a definite physiological 

 balance, that one is capable of absorbing or merging into the other, according 

 as the observer ascends or descends the organic scale. The peritoneal 

 system of fluid terminates at the standard of the insect, the true blood system 

 traced downwards terminates at the Echinodermata. 



Circulating System. — Under this division of our subject we propose to 

 consider only the central apparatus of the true blood-circulation in the Anjie- 

 Uda, postponing the study of the periphery of this system to the time when, 

 in the order of our arrangement, the branchial, pedal and tentacular appen- 

 dages shall have to be described. 



To Prof. Milne-Edwards is due the merit of having first contributed to 

 science a systematic and exact exposition of the circulating system of the 

 worms. Preceding and contemporary anatomists had indeed offered at 

 different times detached and ill-digested observations on this branch of com- 

 parative anatomy. Elaborate memoirs on the organization of some species 

 of Annelida from the pen of M. Quatrefages, have recently appeared in the 

 * Annales des Sciences Naturelles*.' From the conclusions and descriptions 

 of this naturalist, the author of this Report will have frequent occasion very 

 materially to diff'er. In the following account, which will be drawn almost 

 entirely from original observations, no order will be observed in the selection 

 of examples. So great is the simplicity of the plan on which the main vas- 

 cular trunks, constituting the central apparatus of the circulation in Annelids, 

 are arranged, that a few general statements, expressive of leading constructive 

 principles, will be found not inapt as introductory to the study of details : — 



1st. In all Annelids the blood flows in the great dorsal trunk from the tail 

 towards the head. 



2nd. In all Annelids the blood flows in the great ventral trunk from the 

 head towards the tail. 



3rd. In the whole integumentary system of vessels the blood moves from 

 the great ventral towards the great dorsal trunk ; this movement constitutes 

 the annular or transverse circulation. The main current of the blood in the 

 ventral trunk pursues a longitudinal course until exhausted by successive 

 lateral deviations. 



ith. In the majority of Annelids the intestinal system of vessels consists of 

 four longitudinal trunks : one dorsal, which may be called dorso-intestinal ; 



* Etudes sur les types inferieurs de rembranchement des Annelides, par M. de Quatre- 

 fages ; et Memoire sur la famille des Hennellieus, S"'^ serie, 1848. 



