OF THE COLD-BLOODED VEHTEBRATA. 221 



Mibie-Edwards*, Huxley t, M'Leay |, Vogt§, and otlier naturalists 

 of at'kuovvledged competeucy, miglit all be cited iu favour of the 

 view here advocated. 



It is indeed true that we know not the embryology of the 

 extinct genera Lahyrinthodon and Archegosaurus ; but negative 

 evidence of this kind can scarcely be said to have much value. A 

 more valid objection is, that the exo-skeleton of some undoubted 

 Reptiles (for example, Iclitliyosaurus) exhibits certain characters iu 

 common both with Amphibians and true Tishes ; yet these cha- 

 racters are overborne by others to which greater weight must still 

 be attached. Persons prone to speculation will doubtless imagiue 

 fossil skeletons presenting features intermediate between those of 

 the two groups whose affinities are now imder consideration. Such 

 extinct forms may exist, but they have not yet found a place in any 

 osteological museum. 



The second of the two preceding propositions, namely, the pos- 

 sibility of distinguishing between Amphibians and true Fishes, now, 

 in its turn, claims our attention. 



Before the recognition of such genera as Lepidosiren and Arche- 

 gosaurus, this question would not have appeared one of much 

 difficulty ; but the cautious zoologist of our own day hesitates 

 before answering it in definite terms. 



Admitting, with Professor Owen, that the skeleton of Arcliego- 

 saurus indicates the nearer affinity of its possessor to the Pereuni- 

 branchiate Batrachians than to any known Fish, and dismissing, 

 therefore, that singular genus from the category of animals whose 

 class is doubtful, the above question may be re-stated thus : — Wliat 

 conclusion must be drawn from a careful consideration of the 

 totality of organization presented by Le^idosii^en ? 



It is lumecessary here to recapitulate at length those great 

 facts in the anatomy of Leindosiren with which zoologists in 

 general are familiar. Let it suffice to notice briefly most of those 

 peculiarities which seem to bear on its disputed affinities. 



The scaly covering of Le])idosiren, the structure and appearance 

 of the greater part of its skeleton, the relative positions of the anal 

 and lu-o-genital apertures, the conspicuous lateral line, and the 



* ' Zoologie.' Huiti^me edition. Paris, 1858. 



t Seethe second of his *' Lectures on General Natiu'al History," pubhshcd iiv 

 the Medical Times and Gazette, May 17, 1856. 

 X Horce Entomological. London, 1819-21. 

 § Zoologischo Briefe. Fraukfui-t am Main, 1851. 



