32 M. de Quatrefages on the Organization of 



ing upon general physiology than upon the special history of the 

 polyps. 



A third series of researches by the same author has been de- 

 voted to the study of the organization of the Annelida, with a 

 view of determining how the dominant type of that natural group is 

 modified or lowered either in the inferior species, or in those worms 

 which have been ranked by many zoologists among the Entozoa. 

 He has ascertained, in examining the comparative anatomy of the 

 nervous system in Eunice, Nereis, Phyllodoce, Glycera, and some 

 other newly discovered genera, that the ganglionic system is far 

 more complex than has been supposed, and exhibits specific mo- 

 difications analogous to those which have been observed in Insects 

 and Crustacea. 



The vascular system in all the Annelida studied up to the pre- 

 sent time by anatomists has been found to present a very consi- 

 derable amount of development. In some however, as in certain 

 Tubicolce, M. Quatrefages has proved that the circulation is not 

 performed by vessels, but through lacunse situated between the dif- 

 ferent organs : thus, in a species of Amphicora, very nearly allied 

 to that discovered by M. Ehrenberg, the blood, easily recognisable 

 from its green colour, is not inclosed in vessels, but between the 

 subcutaneous muscular layer and the kind of mesentery that en- 

 velopes the alimentary canal ; and lastly, in a new genus of Anne- 

 lida Errantia allied to Syllis, and called by our author Doyeria, 

 there exist only imperfect rudiments of a vascular apparatus, 

 which is reduced to a simple dorsal vessel. 



The genus Aphlebine of M. Quatrefages furnishes another 

 striking example of such organic degradation. In the ordinary 

 Annelida the circulation is performed as in the higher animals, by 

 the alternate contraction and dilatation of a part of the vascular 

 system ; but in the present genus, the blood, instead of being pro- 

 pelled by any organ analogous to a heart, is set in motion by the 

 repeated strokes of a series of microscopically minute palettes, 

 which are composed of vibratile cilia united in that form, and 

 placed upon the walls of the visceral cavity behind the base of 

 each foot. An analogous mechanism has been observed by Milne 

 Edwards in the Beroes. 



The affinity of internal structure which previous observers had 

 perceived to exist between the Annelida and Rotatoria has been 

 rendered still more intimate by another discovery of M. Quatre- 

 fages, who found upon the coasts of Brittany an Annelide much 

 resembling in general conformation a young Syllis, but which sup- 

 ported upon either side of its body a series of locomotive organs 

 analogous to the vibratile discs of the Rotifers, and so disposed as 

 to simulate when in motion the revolutions of a paddle-wheel. 

 The feet in this singular Annelide, designated by the name of 



