212 REPORT — 1851. 



owe their beauty of form to a series of compressed foliaceous lamellae, which 

 attain in some species a considerable size, and which in all elegantly garnish 

 the sides of the body. The office of these appendages has already been 

 described as that of ' breathing ; ' they are well fitted, however, to aid in 

 progression through water. Following the motion of the feet, and capable 

 of being partially altered from a horizontal to a perpendicular position, they 

 operate as a brush of oars, and must pi-ove especially useful when the worm 

 glides from a solid surface, and finds itself unsustained in the water. Hence 

 the species are quick and lively, and swim with great mechanical facility. 

 " Currit egregie ; natare etiam valet lamellis suis retroversis oblique sursum 

 erectis," says old Fabricius of them in his ' Fauna Grcenlandica.' The occi- 

 put and snout are armed and ornamented by cylindrical tentacles, which are 

 the modified homologa of the lamellae of the feet. Observing the habits 

 of these worms, it becomes at once obvious that these appendages are acute 

 organs of touch. 



In all the Phyllodoce the feet are uniramous. There is only one seti- 

 ferous process, and this is capable of elongation and retraction as usual. 

 The brush of bristles is always situated between the dorsal lamella and 

 the blunt ventral cirrus. The setae are jointed in all species (see figs. 

 37 and 38). The joint is apparently constructed on the ball-and-socket 

 principle. The base of tlie extreme piece is enlarged into a small knob, 

 while the end of the shaft is hollowed into a cavity, into which the former 

 accurately fits. These two parts are really tied together by means of a 

 ligamentous membrane extending from the margins of the acetabulum round 

 and over the ball, to embrace the stem ; and yet it is not a true articula- 

 tion ; its action is due to elasticity, not to any muscular voluntary agency. 

 In P. viridis, one admirably adapted for walking on solid surfaces, the 

 extreme articulated portion, pointed to the acuteness of a needle, is first 

 firmly fixed on the unhinged surface: the other now lifts the body of the 

 animal forwards, moving upon this as a fulcral pivot. In an undescribed 

 species, the stem of the seta at its distal end and on the under side, is 

 •' roughened " with strong teeth, for pushing purposes. Other minor varie- 

 ties in the structure of the bristles occur in other species. In P.lamelligera, 

 the most attractive of all, a second foliaceous lamella is superadded to the 

 respiratory one, and the setiferous process is ventralmost in situation. The 

 tail in the Phyllodoce, without exception, is provided with two flattened 

 styles, which exceed in size by three or four times the lateral appendages, 

 and which act on the principles of the caudal fin of the fish in sculling and 

 helming. It is a remarkable fact, proving their true homology, tliat the 

 styles in the Annelids, wherever they exist, are formed on the model of the 

 lateral cirri. When these last are blunt and clavate, as in a new species 

 which the author has lately established, the former are blunt and clavate 

 accordingly ; when acute and flattened, the latter are so also. The styles, 

 however, are always considerably larger in dimensions than the lateral cirri. 

 This correspondence of plan does not, indeed, obtain between the tentacles 

 and the lateral appendages. The former are nearly round and tapering, while 

 the latter may be flat. 



An exception to this rule occurs in the Syllidce, in Avhich the two orders 

 of appendages present the same character. In this interesting genus the 

 appendages are distinguished for their extreme length and slenderness. 

 The feet are uniramous or undivided. The superior cirrus it is, which 

 by its unusual length and tasteful figure and easy movements, procures for 

 these little Annelids their charm for the eye. Elongate and submouiliforra 

 throughout their entire length in S. armillaris, S. maculosa, and PsamathCf 

 these branchial cirri are beaded only through the distal half of their length. 



