CONVERGENCE IN EVOLUTION 259 



type of structure, we can theoretically suppose 

 that it will be reached in the course of time by the 

 selection of variations, along two or more distinct 

 routes. In some cases, however, it is an assumption 

 to say that the type of structure attained is the 

 only possible solution of the problem, or by far 

 the best and easiest. Moreover, the difficulty of 

 Darwinian interpretation increases a little when the 

 mode of individual development is quite different in 

 the two cases, and when the similarities include 

 minute details. The striking superficial resemblance 

 between burrowing amphibian, burrowing lizard, 

 and burrowing snake a familiar puzzle to students 

 of elementary zoology is readily intelligible, for 

 the worm-like shape is the only one possible; but 

 is there not more difficulty in accounting for the 

 telescope eyes of unrelated fishes and cuttlefishes, 

 where the general idea is the same, though there 

 are marked differences in deail and in development? 

 Some thoughtful students of evolution * see no 

 special riddle in the attainment of closely similar 

 adaptations by unrelated types. But as we do not 

 regard with much satisfaction or confidence the 

 available biological interpretations of the way in 

 which creatures of very diverse flesh and blood 

 have often worked out the same solution to 

 a problem, we would make three suggestions. 

 ( i ) There are probably architectural laws of growth 

 and differentiation of which we have not more than 



1 See for a clear-headed discussion a letter by Mr. George 

 Hookham in The New Statesman, 6th Jan., 1917, p. 325. 



