VII.] SPECIES AND SPACE. 167 



tiles, and as the beak of the cuttle-fish or of the tadpole 

 resembles that of birds. We have already seen (in Chapter 

 III.) that it is impossible, upon any hypothesis, to escape 

 admitting the independent origins of closely-similar forms. 

 It may be that they are both more frequent and more im- 

 portant than is generally thought. 



That closely-similar structures may arise without a 

 genetic relationship has been lately well urged by Mr. Ray 

 Lankester. 18 He has brought this notion forward even as 

 regards the bones of the skull in osseous fishes and in mam- 

 mals. He has done so on the ground that the probable 

 common ancestor of mammals and of osseous fishes was a 

 vertebrate animal of so low a type that it could not be sup- 

 posed to have possessed a skull differentiated into distinct 

 bony elements even if it was bony at all. If this was so, 

 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 independent 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 arrangements and very 

 different magnitudes." 19 And no investigator of homologies 

 doubts that a considerable number of the bones which form 

 the skull of any osseous fish are distinctly 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 the most remote 

 genetic affinity, it would be rash to affirm dogmatically that 

 there is any impossibility in the independent origin of such 

 forms as centetes and solenodon, or of genetically distinct 



18 See Ann. and Mag. of Xat. Hist., July, 1870, p. 37. 



19 Prof. Huxley's Lectures on the Elements of Comp. Anat., p. 184. 



