40 THOMAS HENRY HUXLEY 



XLViii, p. 517). The suggestions made by the author 

 in the last memoir as to the affinities of these extinct 

 types is repeated with rather more emphasis, on the 

 strength of further evidence. The view tentatively 

 advanced would not now be accepted, but the difficulty 

 of the matter is fully realized, and there is a marked 

 absence of dogmatic statement, 



3. "On a New Species of Plesiosaurus, etc." (Q. J. 

 Geol. Soc, xiv, 1858, pp. 281-94. Sci. Mem., i, 

 XLix, p. 522). — This technical comparative memoir is 

 an important contribution to our knowledge of a 

 remarkable group of swan-necked marine reptiles which 

 were dominant during the Mesozoic epoch. 



4. "On Some Points in the Anatomy of Nautilus 

 pompilius" (J. Linn. Soc. (Zool.), iii, 1859, pp. 36-44. 

 Read June 3, 1858. Sci. Mem., ii, iii, p. 81). — This is 

 an addition to our knowledge of the pearly Nautilus, the 

 last survivor of a long series of extinct types. 



5. " On the Theory of the Vertebrate Skull " (Proc. 

 Roy. Soc, ix, 1857-9, PP- 3^1-457 » Annals and Mag. 

 Nat. Hist., iii, 1859, pp. 414-39. Sci. Mem., i, l, 

 p. 538). — Here we have an epoch-making memoir, which 

 is in substance the Croonian lecture delivered before 

 the Royal Society, June 17, 1858. It completely 

 demolishes the transcendental theory of Oken that the 

 skull is in reality composed of three modified vertebrae, 

 and is therefore equivalent to a modified piece of 

 the backbone. The facts of comparative anatomy and 

 embryology are marshalled in a masterly fashion against 

 this conception. At the same time the speculative views 

 of Owen, founded upon those of Oken, are subjected to 

 destructive criticism. 



This precluded any settlement of the rupture which 

 had taken place the previous year between the two 



