ON THE BRITISH ANNELIDA. 179 



pulmonary hearts, form in reality the edge of the utero-ovarian organ (fig. Q,f) 

 The walls of these fusiform hearts are described as muscular, highly irritable, 

 and perforated only by a small bore. The error of this description is so 

 flagrant, that we are constrained to stop, that we may indulge in one more 

 expression of surprise, that English authors for a period of twenty-three 

 years, and that in the epoch of the microscope, should have lent themselves 

 to the propagation of statements so diametrically at variance with nature. 

 The detailed description of these parts will belong to that division of this 

 memoir which treats of the reproductive organs of the Leech ; to this source 

 the reader is accordingly directed for full information. 



In addition to the main dorsal and ventral trunks, there exists in this An- 

 nelid and in the Earth-worm, two strong and obvious lateral trunks, one on 

 each side (fig. 6, e, e), as to position and size, correctly enough described 

 by Duges under the appropriate name of latero-abdominal vessels ; the 

 remarkable structure of these vessels has, however, altogether eluded the 

 observation of M. Duges. In his account they are described as ordinary 

 vessels, while the branches proceeding from them are represented as furnished 

 with very strong muscular parietes. Our researches have led us to conclu- 

 sions directly the reverse of those of M. Duges. The branches exhibit in 

 their walls a structure precisely the same as that which distinguishes the 

 vascular system in every other part of the body, while the primary lateral 

 trunks are provided with remarkable muscular parietes, the fibre of the 

 muscle being of the striped kind. The fascicle of the muscle composing the 

 walls is arranged in a manner which is quite distinctive of and peculiar to 

 this vessel (see fig. 6, e, e) ; it is coiled with so much regularity as to en- 

 close a perfect cylinder, in which the blood flows ; the longitudinal fibres are 

 almost entirely suppressed ; the circular fascicles, lined within by a hyaline 

 membrane, constitute therefore the exclusive coat of the vessel ; such a ves- 

 sel is almost unique in structure in the animal series, but none other would 

 perform so admirably the peculiar duties for which it is introduced into this 

 part, obviously as a special provision. Its business is to transmit with aug- 

 mented force a current of blood, in a transverse direction, from the side to 

 the utero-ovarian organs ; these organs form a double longitudinal series, one 

 on either side of the ventral mesial line* in each annular segment of the 

 body. An express branch from the latero-abdominal trunk on either side is 

 rendered to these reproductive organs (fig. 6, h) ; so that the amount of blood 

 propelled by this vessel, measured in its totality, must be very considerable ; 

 and the quantity, during the generative season, must undergo great increase, 

 in consequence of the augmentation of size which at this period these organs 

 experience. The lateral longitudinal vessel is strikingly adapted ta meet 

 such alternations of extremes ; constructed of muscle, it readily yields under 

 the_/?ow of the blood-tide to the organs to whose wants it ministers ; and 

 constructed of muscle, its parietes augment by accelerated nutrition during 

 the periods of increased local determination of blood ; formed of any other 

 structure than muscle, such admirable adaptive alternations could not happen. 



In the dissections of Quatrefagesf, the great dorsal trunk in the Leech is 

 correctly represented as common to the integument and intestine. In con- 

 sequence of the layer of pigmental glandular cells by which all the vessels 

 in this Annelid are enveloped, to trace their courses individually is rendered, 

 practically, very difficult. 



The Earth-worm exhibits a vascular system (Plate III. fig. 7), of which the 

 plan coincides in a remarkably intimate manner with that of the Leech. This 

 correspondence between the circulatory systems of these two Annelids arises 



* Vide Reproductive Organs, &c. t Begne Animal, Vol. Anmlides. 



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