Prof. E. Claparede on the Structure of the Annelida. 349 



Perivisceral Cavity and Circulatory System. 



We are indebted to M. de Quatrefages and Dr. Williams, but 

 especially to the former, for a profound investigation of the 

 perivisceral cavity and of the lymph which it contains. These 

 naturalists, more than any one else, have pointed out the physio- 

 logical importance of this liquid, which cannot be too highly 

 estimated. Some details, only, require a slight rectification 

 here. The periviscei-al cavity is lined by a delicate membrane, 

 which is not easily demonstrable, except in the larger species — 

 a membrane the discovery of which M. de Quatrefages ascribes 

 to himself, and to which he gives the name oi peritoneum. Had 

 he thoroughly explored the works of Delle Chiaje and Rathke, 

 he would have found in them both the membrane and the name. 

 The structure of this peritoneum {tunica sierosa, tunica peri- 

 toneale of Delle Chiaje) is subject to considerable variations, as 

 I shall show in the course of this memoir. At any rate, the 

 perivisceral cavity is clothed, in some species, with vibratile cilia 

 borne by the peritoneum. If I am not mistaken. Dr. Sharpey 

 was the first to describe these, in ApJirodita ; Dr. Williams then 

 detected them in the branchiae of the Glycene; and I described 

 them as occurring in the whole of the perivisceral cavity of the 

 latter worms. They have also been seen in the Tomopteridea. 

 M. de Quatrefages, who only notices in passing the observation 

 of Dr. Williams, adds that this ciliary movement was long since 

 known to him in a great number of Annelida, and that it will 

 be met with in all the species, if we take the trouble to look for 

 it. This opinion is not well founded. The immense majority 

 of the Annelida present no ciliary movement in the perivisceral 

 cavity, except at the entrance to the segmental organs. For 

 my own part I am acquainted with the perivisceral ciliary coat 

 only in the following groups : — in all the Aphroditea, Ghjcerea, 

 and Polycirrida, in the Tomojjteridea, and in a small and rather 

 abnormal Terebella {T. vestita). It is a striking circumstance 

 that all these Annelida, with the exception of the little Terebella 

 and Aphrodita aculeata, are completely destitute of vessels. 

 Now, of these two exceptions, one {t\\e Aphrodita) is an animal 

 with a rudimentary vascular system, belonging to a family which 

 is otherwise entirely anangian ; the other, the Terebella, belongs 

 to a family which is generally vascular, but one tribe of which, 

 that of the Polycirrida, is anangian. Considering these facts, 

 I must regard the perivisceral ciliary movement as a function 

 vicarial of the circulation in Annelida deprived of a true circu- 

 latory system. 



The circulation of the Annelida has been most carefully de- 

 scribed by M. de Quatrefages, who at the same time renders full 



