ANNULATA. 245 



The blood-vessels, the afferent and efferent, run close to and parallel 

 with the inferior border of the process ; the upper part of each is 

 composed of a membranous lobular addition to the inferior and vas- 

 cular portion. Into the cells of this lobule the chyle-aqueous fluid 

 slowly finds its way, and participates obviously in the office of re- 

 spiration. In N. coniocephala it is remarkable that the cilia should 

 be limited in their distribution to the margin, along which the true 

 blood-vessel runs. This fact is less manifest in ^V. vulgaris, in conse- 

 quence of the smallness of the membranous lobule. In Aricia Cu- 

 vieri the branchial appendages are more conical in figure, more 

 vertical in position, and developed only at the posterior four-fifths of 

 the body. They are covered with large vibratile cilia, which likewise 

 extend over that segment of the dorsum which separates the bases of 

 the branchias. Like those of the preceding genera, they are supplied 

 with spongy tissue for the exposure of the peritoneal fluid. 



" It may have been remarked, that in all the members of the pre- 

 ceding family the real branchial organ has consisted of an evolved or 

 exaggerated development of the superior element of the dorsal foot. 

 In the genus Xephthys, which comes now under review, it is the in- 

 ferior element of the dorsal foot which becomes the subject of this 

 evolution. Nephthys Homhergii of our coasts is a remarkably vigor- 

 ous and active worm, and yet its organ of breathing consists only of a 

 comparatively small curved ciliated process, situated under cover of 

 the dorsal foot, and carrying only a single-looped vessel. It may be 

 mentioned, as an interesting proof of the real appropriation of this 

 process in Nephthys to the function of breathing, that the same 

 process, although similarly shaped, on the ventral or inferior foot, is 

 7iot provided with cilia, nor is it penetrated by any blood-vessel. 



" The genus Cirrhatulus of Lamarck, and the allied group consti- 

 tuted by Savigny under the name of Ophelia, introduce to the phy- 

 siologist another modification of the branchial organs within the 

 limits of the dorsibranchiate order. As in the preceding families, 

 they are in these latter only ' developments ' of the dorsal cirri. In 

 Cirrhatulus Lamarckii, a linear series of yellowish and blood-red 

 threads, remarkably irritable and contactile, project to a considerable 

 distance, from each side of the body, thoughout its whole length; at 

 the occiput, however, they are arranged in a crown-like form. These 

 beautiful filaments, which are obviously designed to fulfil the twofold 

 office of touch and respiration, appear under the microscope to con- 

 sist only of a single blood-vessel inclosed in a delicate sheath of inte- 

 gument. Closer analysis, however, discovers two vessels in each of 

 these filaments, and traces of longitudinal and circular muscular fibres 

 in the investing sheath. By the contraction of this sheath, the iu- 



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