VII.J SPECIES AND SPACE. 173 



hypothesis, to escape admitting the independent origins 

 of closely similar forms. It may be that they are both 

 more frequent and more important than is generally 

 thought. 



That closely similar structures may arise without a 

 genetic relationship has been lately well urged by Mr. 

 Kay Lankester.^ He has brought this notion forward 

 even as regards the bones of the skull in osseous fishes 

 and in mammals. He has done this on the ground that 

 the probable common ancestor of mammals and of osseous 

 fishes was a vertebrate animal of so low a type tliat it 

 could not be supposed to have possessed a skull differen- 

 tiated into distinct bony elements — even if it was bony 

 at all. If the ancestral cranium was thus undifferentiated, 

 then the cranial bones must have had an independent 

 origin in each class, and in this case we have the most 

 strikingly harmonious and parallel results from indepen- 

 dent actions. For the bones of the skull in an osseous fish 

 are so closely conformed to those of a mammal, that " both 

 types of skull exhibit many bones in common," though 

 " in each type some of these bones acquire special arrange- 

 ments and very different magnitudes." ^ And no investi- 

 gator of homologies doubts that a considerable number 

 of the bones which form the skull of any osseous fish 

 are certainly homologous with the cranial bones of man. 

 The occipital, the parietal, and frontal, the bones which 

 surround the internal ear, the vomer, the premaxilla, 

 and the quadrate bones, may be given as examples. 

 Now, if such close relations of homology can be 

 brought about independently of any but tlie most remote 



1 See Ann. and Mag. of Nat. Hist., July 1870, p. 37. 



^ Professor Huxley's Lectures on the Elements of Comp. Anat. p. 184. 



