200 REPORT — 1851. 



is a remarkably vigorous and active worm, and yet its organ of breathing 

 consists only of a comparative 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 not provided with cilia, 

 nor is it penetrated by any blood-vessel. 



The genus Cirrhatulus of Lamarck, and the allied group constituted by 

 Savigny under the name of Ophelia, introduces to the physiologist another 

 modification of the branchial organs within the limits of the dorsibranchiate 

 order. As in the preceding families, they are in these latter only ' develop- 

 ments' of the dorsal cirri. In Cirrhatulus Lamarckii (fig. 19, a, «), a linear 

 series of yellowish, and blood-red threads, remarkably irritable and contrac- 

 tile, project to a considerable distance, from either side of the body, through- 

 out 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 

 consist only of a single blood-vessel enclosed in a delicate sheath of integu- 

 ment. Closer analysis, however, discovers ttvo vessels (fig. 19, a") in each 

 of these filaments, and traces of longitudinal and circular muscular fibres in 

 the investing sheath. By the contraction of this sheath, the enclosed vessels 

 may be completely emptied of their blood from one end of the filament to 

 the other. This contraction does not take place simultaneously in every 

 part, but undulatorily, the wave motion beginning at the extreme fore-end. 

 It is especially to be noted, that, in this variety of appendage, in which the 

 respiratory is only an incidental function, there exist 7io vibratile cilia. These 

 organs in Ophelia coarctata exhibit analogous characters, while they are less 

 numerous and much shorter*. The Aphroditacea constitute a group of An- 

 nelids to which the term " dorsibranchiate " by no means correctly applies ; 

 that is, in the majority of the species embraced in this order no branchial 

 appendages exist either on the dorsum, or any other part of the body. Respi- 

 ration is performed on a novel principle, of which no illustration occurs in 

 any other family of worms. In all Aphroditacece the blood is colourless. 

 The blood-system is in abeyance, while that of the chyl-aqueous is exagge- 

 rated. Although less charged with organic elements than that of other 

 orders, the fluid of the peritoneal cavity in this family is unquestionably the 

 exclusive medium through which oxygen is absorbed. The true Aphrodite 

 type of respiration occurs in Aphrodita acideata. In this species the tale of 

 the real uses of the ' elytra' or scales is plainly told. Supplied with a com- 

 plex apparatus of muscles, they exhibit periodical movements of elevation 

 and depression. Overspread by a coating of felt readily permeable to the 

 water, the space beneath the scales during their elevation becomes filled with 

 a large volume oi filtered water, which during the descent of the scales is 

 forcibly emitted at the posterior end of the body. It is important to remark 

 that the current thus established laves only the exterior of the dorsal region 

 of the body. It nowhere enters the internal cavities; the latter are every- 

 where shut out by a membranous partition from that spacious exterior 

 enclosure bounded above by the felt and the elytra. In this species the peri- 

 toneal chamber is very capacious, and filled by a fluid which only in a slight 

 degree contains organized particles. The complex and labyrinthic appen- 

 dages of the stomach We floating in this fluid, and in the chambers which 



* I have recently discovered several new species in which the branchiae assume the fili- 

 form shape and structure as described in the text, and of which the position in the AnneU- 

 dan scale should be near that of Cirrhatulus. 



