EMBRYOLOGICAL PROBLEMS. 26 I 



progressively less importance as we ascend to the typically 

 terrestrial Amphibia. He also assumes, though no evi- 

 dence is given for it, that as the lateralis branches 

 decrease in size the proper trigeminus branches increase 

 and considers this to be a case of substitution of function, 

 the general cutaneous branches compensating for the loss 

 of the lateralis. The lateral line branches, Pinkus thinks, 

 are the older and in higher forms have been supplanted by 

 the general cutaneous. 



This, I think, is a direct inversion of the actual relations. 

 The general cutaneous fibres are unquestionably the older 

 and are present throughout the fishes and Amphibians in 

 sufficient numbers to innervate the entire cutaneous sur- 

 face amply, and that, too, in cases where the lateralis 

 system attains its maximum development. The latter 

 system disappeared as it came, without materially affect- 

 ing the general cutaneous system, but wholly in relation 

 to the grade of organization of the corresponding sense 

 organs. 



IV. — Embryological Problems. 



The clearest light upon these questions of metamerism 

 will, I think, ultimately come from the embryological 

 side, though so far, it must be confessed, this light has 

 proved, in many cases, a false beacon. The reason is not 

 far to seek, for, as has been pointed out by Cole {'98) the 

 embryologists have not as a rule been able to follow the 

 fate of the structures which they have discovered up to 

 adult life and in most cases the exact anatomical struc- 

 ture of the adult organs of the types studied is unknown. 

 Thus the brilliant speculations of Kupffer ('94) respecting 

 the relation of the epi-branchial and supra-branchial sense 

 organs to the terminal bud and lateral line systems of 



