ON THE BRITISH ANNELinA. 181 



munications between the dorsal and ventral trunks ; in them the blood sets 

 vertically downwards from the dorsal to the abdominal vessels. In other 

 vertical vessels situated more posteriorly and parallel to the so-called monili- 

 form hearts, the blood moves in a converse direction from below upwards : 

 the moniliform character which these vessels exhibit is produced by the pro- 

 cess of dissection. If, in the ordinary way, a longitudinal dorsal incision is 

 made, and the two halves be then separated and pinned down, the vessels under 

 such tension are sure to assume a moniliform outline ; that is, one part will 

 contract, and another will dilate, and so on successively throughout the length 

 of the vessels ; the dilated portion will be filled with blood, and the contracted 

 will be empty, and the beaded figure will be perfect. If, however, a more 

 careful mode of opening the worm be adopted, dividing by means of a fine 

 scissors the membranous segmental partitions, and laying gently open the 

 integuments, these vessels will present a perfectly smootii outline; if now one 

 of them be seized with the forceps and gently pulled, it will become irregu- 

 larly knotted or moniliform. Muscular fibres, chiefly circular, are present in 

 their parietes, and it is to the uneven action of these elements that the beaded 

 fonn is attributable. The contraction of the circular fibres at two points 

 separated by a short interval, imprisoning in that interval a globule of blood, 

 the same conditions occurring at another part, explain clearly the mode in 

 which the moniliform character occurs. Every European writer for the last 

 thirty years has glowed with admiration in describing these "moniliform 

 hearts" in the Earth-worm! And yet even without the refutations of de- 

 monstrative anatomy, how easy, on a little mechanical consideration, would it 

 have been to see that no form of vessel could have been mechanically less 

 adapted for reinforcing the moving power of the blood-current than a conduit 

 composed of a succession of contractions and dilatations ! it is evident that 

 the efficient propeller would be the last dilatation only in the series. A 

 spindle-shaped tube, on the other hand, and muscularly contractile, will be 

 seen to realize all the physical conditions required under such circumstances 

 for imparting a new impulse to the moving current. The latero-abdominal 

 trunks, destined for the supply of the utero- ovarian system, are present in the 

 Earth-worm, and present a structure and relations analogous to the corre- 

 sponding vessels in the Leech ; in the latter, however, the circular muscular 

 fibres are much more developed than in the former, and the vessel is relatively- 

 larger. 



It was imagined by Willis* that he had discovered the existence of a series 

 of pores upon the dorsal aspect of the Earth-worm, which by him were con- 

 strued into stigmata ; and in confirmation of their perforate character, he re- 

 lates that air blown into the openings is dispersed between the integument 

 and intestine, diffusing itself throughout the segmental compartments. It is 

 stated by Duges that he has repeated these experiments with the same results, 

 finding that the pores, instead of terminating in muciparous follicles, as they 

 were supposed to do by many anatomists, penetrate into the interior of the 

 body, so that air injected into one of them passes freely along the segmental 

 chambers which surround the intestine and escape through other neighbour- 

 ing orifices. By these distinguished authors it is further affirmed, that water 

 is imbibed into the segmental chambers through the same orifices, and from 

 which it is given out when the animal is too rapidly dried by exposure to the 

 sun, or irritated by external stimuli. And it is conjectured that aerated water 

 thus taken into the system, and brought immediately into contact with the 

 deep-seated vascular network dispersed over the intestinal parietes, must, 

 therefore, necessarily contribute to the respiratory formation. 

 * De Anima Brutorum, 4to, 1672. 



