248 LEADING AMERICAN MEN OF SCIENCE 



diate service of the brain. Now, among the Crustacea, the 

 Decapoda, as we have seen, have eight pairs of cephalic organs 

 and five pairs of locomotive organs, while the Arthrostraca have 

 six pairs of cephalic organs and seven pairs of locomotive organs, 

 the second and third pairs of maxillipeds in the former group being 

 homologous with the first two pairs of legs in the latter. In like 

 manner, the last pair of oral (cephalic) appendages in Insects 

 the labium is believed to be homologous with the first pair of 

 legs in the Arachnoids. Dana's argument was, accordingly, 

 that the distinction in regard to the use of the anterior limbs in 

 man and other mammals was analogous to the cases cited among 

 the Arthropoda, and that man must therefore be made at least a 

 distinct order in the classification. There is of course no homol- 

 ogy between vertebrate limbs and arthropodan appendages; and 

 Dana's argument, based on a mere analogy, and not a very close 

 analogy, has no force as viewed from the standpoint of zoology 

 to-day. Viewing Dana's discussion of cephalization from the mod- 

 ern evolutionary standpoint, one might make the general criticism 

 that the distinction of high and low, which he emphasized, is 

 of vastly less significance than that of generalized and special- 

 ized. Low forms may be primitive, or they may be degenerate. 

 A vertebrate destitute of limbs would naturally be regarded as a 

 low, or degraded type. But the lamprey is destitute of fins be- 

 cause it is a survival of a primitive type antedating the evolution 

 of limbs, while the snake has lost the legs which its lizard ancestors 

 possessed. Writing before he had adopted the theory of evolution, 

 Dana of course failed to appreciate this distinction. 



Dana was not an early convert to the theory of evolution. It 

 is interesting to compare, with reference to their attitude toward 

 the theory of evolution, the three men who were the leading natu- 

 ralists of this country in the middle of the nineteenth century 

 Gray, Agassiz, and Dana. Gray was ready to welcome the Dar- 

 winian theory when first promulgated. In a letter to Dana in 

 1857, he wrote the prophetic words, " You may be sure that before 

 long there must be one or more resurrections of the development 

 theory in a new form." One year later the prophecy was fulfilled 



