772 HUXLEY AND HIS WORK. 



fishes. (The exact truth was not discovered, but was approximated.) 

 Is it not probable that this memoir was known to Clarke, who claimed 

 to have suggested to Krefft the systematic relations of the newly discov- 

 ered Australian Dipnoan 1 It was creditable to both Clarke and Krefft 

 that they did recognize this relationship and profited by tlieir biblio- 

 graphical knowledge, but it is doubtful whether they would have been 

 able to make the identification or appreciate the importance of the 

 discovery had not Huxley j>artly prepared the way. By this discovery, 

 our acquaintance with the ichthyic faunas of both the present and past 

 was almost revolutionized. 



I • VII. 



To the casual observer none of the terrestrial backboned animals 

 appear to be less related than birds and reptiles. As Huxley remarks, 

 "to superficial observation no two groups of beings can appear to 

 be more entirely dissimilar. - - - Placed side by side, a humming 

 bird and a tortoise, an ostrich and a crocodile offer the strongest con- 

 trast, and a stork seems to have little but animality in common with 

 the snake it swallows." A difference in habits appears to be associated 

 with the difference in form. The activity and freedom of the bird con- 

 trasts with the lethargy and restriction in range of the tortoise — the 

 warm body of the former with the cold mass of the latter. The birds 

 are looked upon as inhabitants of the air, the reptiles as degraded to 

 crawling on the earth. The popular conclusions were to a considerable 

 extent adopted by the scientific, and for a long time the birds and mam- 

 mals were associated together as " warm-blooded " in contradistinction 

 to the reptiles and other vertebrates, which were designated as- "cold- 

 blooded." This classification was in vogue in England when Huxley 

 reopened the question as to the relative affinities of the vertebrates, 

 and in 1804 claimed that the classes of that division " are capable of 

 being grouped into three provinces — (1) the Ichthyoids, comprising 

 Fishes and Amphibia; - - - (2) the Sauroids, - - - compris- 

 ing Eeptiles and Birds; and (3) the Mammals. 1 - - - The Sauroids 

 (afterwards called "Sauropsida") agree in having "a single occipital 

 condyle, a complex mandibular ramus articulated to the skull by a 

 quadrate bone, nucleated blood corpuscles," and thus differ from the 

 mammals, which have " a well-developed basi-occipital - - - ; a 

 simple mandibular ramus articulated with the squamosal and not with 

 the quadratum, with mammary glands and with red non-nucleated blood 

 corpuscles." 



In 1868 Huxley directed his inquiries " on the animals which are 

 most nearly intermediate between birds and reptiles." 2 



The differences between the recent members of the two classes are 



1 Lectures on the Elements of Comparative Anatomy, 1864, page 74. 



2 Annals and Mag. Nat. Hist. (4.), Vol. II, pages 66-75. 



