590 TEE POPULAR SCIENCE MONTHLY 



Starting out, therefore, with three distinct elements, we find them 

 going through a process of change, in the course of which all three 

 evolve products of very similar properties. If we regard this process 

 of disintegration as in the main a reversal of a process of evolution 

 which once took place, i. e., as a process of devolution, we may say, 

 taking, for instance, KaG, ThD, and Act C as the starting points, 

 that these elements commenced a career of spontaneous change, in the 

 course of which transition products were produced which were quite 

 similar to each other ; but ultimately three distinct elements were gen- 

 erated. In the case of the elements, therefore, as in that of organisms, 

 forms which were ultimately to be more or less dissimilar, passed, in 

 the course of their development, through stages in which they closely 

 resembled each other. 



It is still more instructive if we consider the stages in the ontogeny 

 of various animals in reverse order. We should then find, taking the 

 Crustacea, for instance, as examples, that starting out with even the 

 most diverse forms of these animals, and imagining them to go through 

 the stages of their development in reverse order, 21 they would grow 

 more and more similar as they approached the larval stage, and when 

 they reached that condition, would be very much alike at corresponding 

 stages of development ; just as radium, thorium and actinium are much 

 alike at corresponding stages in their degeneration. 



Now, the significance of the embryological phenomena referred to 

 is that these resemblances between animals of quite distinct groups are 

 believed to indicate an ultimate common ancestry for the organisms so 

 related; and since we have observed a condition which we may con- 

 sider comparable to this among the elements, it seems probable that 

 those radioactive elements which exhibit such close similarities as we 

 have described as their disintegration progresses, originated by evolu- 

 tion from a primary simpler substance ; it seems probable, that is, when 

 taken together with the other evidences of evolution herein adduced. 



Even if we disregard analogies, the fact that three distinct elements 

 consistently show marked similarity in properties in the course of their 

 disintegration would lead to the presumption that, if we could follow 

 them back far enough, they might prove to be identical. This pre- 

 sumption is strengthened by the analogy we have considered. 



It may be remarked that the changes occurring during radioactive 

 disintegration are further similar to those which take place in ontogeny, 

 in that in the former, as in the latter, the various stages are not perma- 

 nent, but change continuously into other stages; and these changes are 

 in both cases spontaneous, taking place without the aid of any external 

 agency. 



21 Such a process need not be wholly imaginary, however ; phenomena com- 

 parable to this are found in the instances of so-called retrograde development. 



