Thomas Dwight 227 



the mammalia, but which appear homologous with structures in other 

 vertebrates and indicate a reversion to the common vertebrate type ante- 

 cedent to class distinctions. Less far-reaching are progonal reversional 

 variations in which the observed structure is normal in no species of 

 that order, and consequently points to the common class stem. Ataval 

 reversional variations represent structures which though not normal in 

 the species in question exist in species of the same order. The supra- 

 condyloid process, according to him, belongs to the first of these classes; 

 but the question at issue is, whether this method affords any solution of 

 the difficulty. Xow the possibility of a reversion is not in the slightest 

 established by calling it archeal; on the contrary it may be said that by 

 defining the dimensions of the gulf to be passed the probabilities of a leap 

 over it become less conceivable. In short, according to the general 

 teaching, it seems to be claimed that putting aside alleged progressive 

 variations and such as for want of a better word may be called acciden- 

 tal, there is no principle to account for variations save reversion. But 

 the difficulty is not yet fully stated; for the problem is not to account 

 for the supracondyloid process only, but for all the variations of bone, 

 muscle, viscus, etc., that occur in man or in any animal. So far as they 

 have been studied we do not find any universal concurrence in the evi- 

 dence; and yet it is essential to the theory that there should be no con- 

 tradictions. I have from the first been much impressed by the passage 

 in the late Lord Salisbury's (17) Oxford address concerning Mendeleef's 

 law according to which " elements can be divided into families of about 

 seven, speaking very roughly : that those families all resemble each other 

 in this, that as to weight, volume, heat, and laws of combination the 

 members of each family are ranked among themselves in obedience to the 

 same rule. Each family differs from the others, but each internally is 

 constructed upon the same plan." What was a weakness in this theory 

 "was turned into strength," to quote again his words, by the discovery 

 of certain elements which were wanting in some of the groups when the 

 law was first announced. He continues : " If these were organic beings 

 all our difficulties would be solved by muttering the comfortable word 

 ' evolution ' — one of those indefinite words from time to time vouchsafed 

 to humanity, which have the gift of alleviating so many perplexities and 

 masking so many gaps in our knowledge." Physics not being in my 

 line, I thought it advisable to inquire of an authority whether this were 

 correct, and was assured in reply that ]\Iendeleef s law had been confirmed 

 and strengthened since Lord Salisbury's address and is now used as the 

 working hypothesis. If, then, we have such curious resemblances in 

 non-organic nature, why should the mere fact of life put aside the possi- 



