178 REPORT — 1851. 



exhibits proofs of great complexity, the main currents of the blood obey two 

 leading directions. If the body of the worm be longitudinally bisected by 

 an imaginary, horizontal plane, into a doi'sal and ventral semi-cylinder, then 

 the blood in the primary trunks of the dorsal half will move from the tail 

 towards the head, and in the ventral half from the head towards the tail : 

 this movement prevails equally in the great longitudinal trunks of the integu- 

 ments and alimentary canal. The transverse or circular movement of the 

 blood is performed by means of branches which run between the main lon- 

 gitudinal vessels ; this latter system is divisible vertically into as many por- 

 tions as there are rings in the body of the worm ; each segment of the body 

 under this arrangement has its own independent circulation, transverse and 

 longitudinal. Thus the currents describe two eccentric ellipses, cutting each 

 other at right angles ; of course the segmental divisions of the general system 

 communicate with each other most intimately at every part, while the primary 

 longitudinal trunks are common to all the segments. From this description 

 it is manifestly impossible that a distinction of venous and arterial blood can 

 exist in the circulating system of this Annelid ; in every part of the circum- 

 ference of each ring the blood is being arterialized as it is being rendered 

 venous ; the two opposite processes proceed simultaneously in the same capil- 

 lary system ; the blood must be therefore as arterial and as venous at one 

 and the same time in the dorsal and in the ventral trunks ; the dorsal main 

 is notwithstanding recipient, the ventral distributive of the blood ; all the 

 secondary currents converge upon the former and emanate from the latter ; 

 the blood in both is nevertheless identical in physiological properties. 



A diagram accompanying this Report conveys a correct expression of the 

 principles as now explained (fig. 6). 



There is, however, in the Leech another distinct and almost independent 

 segment superadded to the general circulation, which, since the aera of the 

 memoirs of M. Duges*, has been called the respiratory or pulmonary system. 

 If there existed really in nature what this anatomist has described, most 

 wonderful and admirabe indeed, estimated by the Annelidan type, would be 

 this pulmonary system. The illustrations of the singular vessels composing 

 this " minor circulation " for breathing, as originally given in the memoir of 

 M. Duges, must be familiar to every one who has ever opened a book on 

 zoology ; since every European writer, from the year 1 828, has servilely 

 copied the figures given by M. Duges. M. Quatrefages, in the illustrations 

 published in the last edition (Crochard's) of the ' Regne Animalf ,' has indi- 

 cated the pulmonary hearts of M. Duges as the " poches secretrices laterales 

 avec leurs caecum," an error no less extraordinary than that committed by 

 his eminent predecessor in this branch of comparative anatomy. The fol- 

 lowing description of the minute anatomy of these parts will prove conclu- 

 sively, that these two observers, in whose track all modern anatomists, with- 

 out a single exception, have followed, have imperfectly described what they 

 saw, and saw most incompletely what existed in nature. The curved branches 

 supplying the respiratory sacs J, to which M. Duges has assigned the name of 



* ' Recherches sur les Auuelides Abranches,' Annal. des Sciences Naturelles, t, xv. 



f See Plate 24, Vol. sur Annelides. 



X If the reader will refer to Rymer Joues' ' Animal Kingdom,' Art. Annelida, by Milne 

 Edwards, in the Cyclopaedia of Anatomy and Physiology, or Owen's ' Lectures on Comparative 

 Anatomy,' he will see that the so-called pulmonarj' hearts of Duges, which are represented as 

 thick-walled, fusiform vessels, arising from the dorso-lateral trunk, and breaking into a 

 plexus of capillaries upon the parietes of the so-called respiratory sacs, correspond in outline 

 ■with the upper edge of the utero-ovarian system as figured in the illustration, fig. 6. More 

 than this resemblance of outline, there is uothing in common between the results of the 

 inquiries and the conclusions of Duges. 



