ON THE BRITISH ANNELIDA. 167 



of Terebella. The same line of argumentation applied to the Crustacea has 

 led this naturalist to infer that this class should occupy a place immediately 

 above the Annelida and below Insects ; that thus the Annelida should stand 

 at the bottom of the Annulose series and the Insecta at the summit, the Crus- 

 tacea being intermediate. 



While we are willing to applaud the sagacity of these speculative thoughts, 

 we must persist, in this Report, in adhering to the evidence drawn fromadult 

 rather than embryonic structures, and that on the plea that mature forms in 

 the same sub-kingdom must bear to each other constant and invariable re- 

 lations, and that the perfect animal no less than the transfigurations of the 

 embryo, by the deep written characters of its organism, must attest its true 

 relative position. It will accordingly be maintained in this memoir, that 

 below, the nearest connection of the Annelida are the Entozoa ; that the Si- 

 punculidcB associate them in a direct and natural manner with the Echino- 

 derms, and with far greater intimacy of resemblance in structure than that 

 with which they are joined to the Mollusca by the intervention of the Chi- 

 tonidce, and that above the Annelida should be placed the inferior species of 

 the lulidce. Considerations founded on anatomical evidence will be after- 

 wards advanced confirming the propriety of this distribution. 



It is proposed now to enter at some length upon that division of our Report 

 which relates to the anatomy of Annelida, as an appropriate prelude to a de- 

 tailed study of species. 



Anatomy of the Annelida. — Anatomical details, correctly determined, will 

 be found hereafter indispensable to the classification of the Annelida. These 

 animals, unlike all other inferior tribes, in many instances present so little 

 external diversity among themselves, while their internal organization at the 

 same time may be strongly marked by specific peculiarities, that a careful 

 consideration of the anatomy of the class will here appropriately precede that 

 of its methodical arrangement. Certain leading points in the structure of 

 worms were established by the dissections of the earlier anatomists. The 

 researches of Willis* gave some rude conception of the character of the cir- 

 culation of the blood, and the outline of the alimentary system. By Sir E. 

 Homef this inquiry was prosecuted to some further extent ; and in this path 

 of investigation, this comparative anatomist was followed by M. de Blain- 

 ville J and Morren§. It was about this date that the labours of M. Duges 

 were given to science, by the publication of his memoirs on the circulation 

 and reproductive system of the Annelides||- It is a fact lamentable to relate, 

 that the errors and imperfect dissections of the professor of Montpellier should 

 have been propagated through the classic works of the most distinguished 

 modern authors down to the present time. The account which M. Duges 

 has given of the reproductive organs of the leech and the Nais is full of grave 

 errors, and it will be afterwards proved that those of M. Quatrefages, although 

 nearly fifty years later, are little less remote from the truth of nature. It 

 should have been previously stated, that in the year 1806 a M. Thomas^ had 

 already thrown some light on the anatomy of the leech. The 'Le9ons d'Ana- 

 tomie Comparee ' of Cuvier, edited by M. Dumeril, which appeared about 

 this period, on the subject of the anatomy of the Annelida, contained little 

 more than an epitomized statement of what had been previously published. 



* De Anima Brutorura. f Philosophical Transactions. 



X Dictionnaire des Sciences naturelles, t. Ivii. p. 407. 



§ De Lumbricibus terrestribus historia natnrali necnon anatomia tractatus. Bruxelles 1829. 

 II Recherches sur la circulation, la respiration et la reproduction des AnneUdes abranches. 

 Annales des Sciences naturelles, l'" Serie, t. xv. 1828. 

 1[ Memoire pour servir a I'histoire naturelle des Sangsues, in 8vo, Paris 1806. 



