ON THE BRITISH ANNELIDA. 169 



in suspension, varying in different species, and performing irregular to and 

 fro oscillations under the agency of the muscular contractions of the intestine 

 and integuments. On these two fluids, two separate physiological functions 

 devolve : each is essential to the maintenance of life in the Annelid ; nor is 

 it improbable that the clue unravelled by the study of these fluid elements in 

 this class, will lead to important conclusions in relation to the mechanism of 

 nutrition in all invertebrate animals. All the recesses and ramifications of 

 the general cavity of the body in the Annelids, communicate freely with each 

 other, constituting thus one common space. This cavity is lined by a distinct 

 membrane, which is obviously the anatomical analogon of the peritoneum, and 

 is filled by a fluid which is unquestionably an organic fluid. Reasons will 

 be afterwards adduced for regarding this fluid as phyBiologically allied to the 

 chyle of the higher animals, and the containing cavity as the prototype of the 

 peritoneal. It is therefore proposed in this memoir to distinguish this general 

 splanchnic chamber as the peritoneal cavity, and the contained fluid under 

 the designation of the peritoneal fiuid, or the chyle-aqueous fluid of the 

 peritoneal cavity. In the Annelida, the peritoneal membrane is not vihra- 

 tile; the oscillations of the fluid contents cannot therefore be due to ciliary 

 vibration. This fact distinguishes the Annelid from the Echinodermata, of 

 which the peritoneal space, in all species, even in the SipuncididcB, is richly 

 lined with vibratile cilia. Tliis observation it is only necessary to qualify by 

 the single remark, that in some species of Annelids, as that of Glycera, the 

 hollow interior of the branchice in which the peritoneal circulates is lined 

 with mobile cilia. 



The real characters of this fluid have remained up to the date of the 

 researches of the author of this Report quite unknown to anatomists*. 



* About two years ago he communicated to the Swaaisea Literary and Scientific Society a 

 paper " On the Structure and Habits of the Annelida," in which a summary was presented 

 of the results at which he had then arrived, with respect to the organic and chemical compo- 

 sition of this fluid. In that communication, illustrations of the floating organic corpuscles 

 were also exhibited, and the views, expounded in the text, with regard to the physiological 

 signification of the fluid in the economy of the worm, were first sketched. The author has 

 only recently become acquainted with a memoir, " Sur la famille des HermeUiens," by M. 

 De Quatrefages (Annales des Sciences Naturelles, 3""^ serie, 1848), in which this industrious 

 French anatomist alludes in the following language to the general cavity of the body in the 

 instance of Sabella alveolata : — 



" Chez les Hermelles comme chez toutes les Annelides, et on pent le dire aujourd'hui, comma 

 chez la majorite des invertebres, les teguments et les couches musculaires sousjacentes cir- 

 conscrivent une cavite, dans laquelle est renferrae le tube digestif. Dans les Annehdes en 

 general, dans les Hermelles en particulier, cette cavite n'est pas d'une seule venue. Entre 

 chaque anneau se trouvent des cloisons incompletes fermees par des colonnes musculaires qui 

 s'elevent en s'elargissant, et se soudant de has en haut, de maniere a former en dessus une 

 membrane. Entre le dernier anneau thoracique et le premier anneau abdominal, la cloison 

 est beaucoup plus epaisse et plus complete ; eUe manque, an contraire, entre le deuxieme, et 

 le troisieme anneau abdominal, espece qui correspond an jabot. Dans chaque anneau de 

 I'abdomen considere isolement, la cavite renferme une portion du tube digestif et des organes 

 geuitaux. Sur les cotes, a la hauteur des pieds, cette cavite se prolonge dans I'interieur de 

 ces derniers. Les gaines des soies, les muscles qui les mettent en mouvement, sont entiere- 

 ment Ubres dans ces especes des chambres. La couche de tissus tres dehcats qui tapisse 

 I'interieur des pieds est herissee de grands cils vibratiles. Le mouvement de ces cils est loin 

 d'etre regiilier et constant ; on le voit quelquefois regner dans toute I'etendue de la cavite ; 

 d'autres fois s'arreter entierement ; mais le plus souvent, il est partiel, et se raanifeste tantot 

 sur un point, tantot sur un autre. Malgre le nombre d'observations, tres considerable que 

 j'ai faites sur des Annelides errantes ou tubicoles, c'est la seconde fois seulement que j'ai 

 rencontre des cils vibratiles dans une dependance de la cavite generale du corps. A I'epoque 

 de la reproduction, la cavite dont nous parlous est rempUe par les oeufs ou les spermatozoi'des, 

 qui penetrent jusque dans I'interieur des chambres des pieds. En temps ordinaire, on trouve 

 dans la cavite generale im Uquide parfaitement incolore, au milieu duquel nagent des corpus- 

 cules irreguhers refractant fortement la lumiere, et dont 1^ ngmbre varie dans les divers mdi- 



