19@ BEPORT — 1851. 



tinal sj'stems. The extreme elongation of the body in these worms necessi- 

 tates tlie existence of a central propulsive power, notwithstanding the con- 

 tractile property with which every part of the circulating system is endowed. 

 In these singular worms, the alimentary system of which will be afterwards 

 described, the blood-proper is red in colour, and perfectly devoid of globules 

 of any sort. The peritoneal space, as it exists in most other Annelids, is not 

 to be found in these genera, since the alimentary organ superadded to the 

 proboscis and oesophagus is adherent to the general integument. 



A general idea has now been given of the central agents of the circulation 

 of this class of invertebrate animals. The special elaboration of the circum- 

 ferences of this apparatus to meet the exigences of local and special func- 

 tions, will be further considered in describing the ultimate structure of the 

 several gland-organs of the body. Over the intestine the blood-vessels ramify 

 in accordance with a special plan of subdivision. This observation applies 

 also to all the other constructional elements of the organism : each is provided 

 with its peculiar order of blood-vessels. A subordinate system of blood- 

 vessels, distinct and remarkable in its anatomical relations, is susceptible of 

 demonstration in all Annelids in which the peritoneal fluid exists. These 

 vessels may generally be distinguished by their coiled length, perfect naked- 

 ness, and floating in the fluid of the cavity, and liwbranching (see again fig. 

 8, g,g,g). And, finally, it must impress the physiologist with surprise, that 

 amid so great apparent complexity of arrangement in the blood-vessels of the 

 Annelida, it should be possible to reduce the movement of the blood to a 

 single definite orbit of remarkable simplicity. The anatomical details now 

 presented suffice to establish the general propositions formerly enounced, 

 which indicated only two circles of motion, longitudinal in the primary trunks, 

 circular in the secondary. 



Integumentary System. — The integumentary system will anatomically in- 

 clude a consideration of the whole apparatus of the appendages, wherever 

 these latter are found to exist. In the organization of the Annelida, no part 

 presents such constancy and fixity of character as the hard elements of the 

 appendages. They constitute the least fallacious ground for the classifica- 

 tion of species. The soft elements, on the contrary, are liable to endless 

 variations from age and the accidents of growth. The appendages in all 

 cases are true productions of the integ\unentary structures. In no instance 

 do they exhibit any connexion whatever with the visceral and intestinal 

 systems. All Annelida are comprised in the twofold division of Branchiata 

 and Abranchiata ; this however is neither an unobjectionable nor a convenient 

 distribution. Several species exist, of which the soft pedal appendages do not 

 contain a specially organized branchial element: this remark is true of all the 

 Syllidce. The proposition is notwithstanding not difficult of anatomical 

 proof, that the Annelida are really divisible into those which have and into 

 those which have not external and apparent branchial organs. M. Dumeril 

 had realized a clear conception of the practicableness of such a division, 

 when he proposed the terms Cryptobranchia and Gym7iobra?ichia as expressive 

 of this bipartite arrangement. Far-sighted and sagacious as must have been 

 the views which suggested this general proposition, the word Cryptobranchia 

 involves an anatomical untruth : there exists no species in which the branchiae 

 are internal or concealed. Respiration in all those destitute of external 

 appendages is performed internally, but not by any specially constructed 

 organs. This function, under such circumstances, devolves either upon the 

 general walls of the alimentary canal or external surface of the body, as in 

 the Borlasiudce, Gordiusida. ; or it is enacted by the fluid, which, in nearly 

 all the Abranchiate genera (except the Leech and the Earth-worm), occupies 



