244 NATURAL SCIENCE. j„^h. 



teeth, are substantial advances of which tlie importance cannot be 

 over-estimated. 



The researches of Professor W, K. Brooks and Mr. F. H. 

 Herrick, of which a general preHminary account appears in the 

 April Johns Hopkins University Circular, seem to have an especially 

 important bearing on certain current doctrines in Evolution. If these 

 authors' interpretation of the facts in the observed life-history of 

 several highly organised Crustacea be correct, it would appear that 

 a single specific type of animal may result from the development of 

 two or more different series of immature stages — that either the life- 

 history of the individual does not always recapitulate the history 

 of the race, or else that any existing type of life may have been 

 evolved from several distinct but gradually converging series of 

 ancestors. We cannot do better, indeed, than quote from the 

 Report to show the nature of the evidence: — 



" One of the most remarkable results of our study of the various 

 species of the genus Alphens is the discovery that, while there is such 

 a general similarity as we might expect between the larval stages of 

 the different species, the individuals of a single species sometimes 

 differ more from each other, as regards their metamorphosis, than the 

 individuals of two very distinct species. 



" This phenomenon has been observed by us and carefully 

 studied in two species, Alphens hetcrochelis and Alphens sanlcyi. ... In 

 the case of the first species, the difference seems to be geographical, for 

 while all the individuals-which live in the same locality pass through 

 the same series of larval stages, the life-history of those which are 

 found at Key West is very different from that of those which live on 

 the coast of North Carolina, while those which we studied in the 

 Bahama Islands present still another life-history. In the case of the 

 second species, A . sanlcyi, the difference stands in direct relation to 

 the conditions of life. The individuals of this species inhabit the 

 tubes and chambers of two species of sponges, which are often found 

 growing side by side upon the bottom, and the metamorphosis of 

 those which live in one of these sponges is quite different from that 

 of those which inhabit the other. In this species the adults also are 

 different from each other, but as we found a perfect series of transi- 

 tional forms there is no good reason for regarding them as specifically 

 distinct, and in the case of the other species, A. heierochelis, we were 

 unable, after the most thorough and minute comparison, to find any 

 difference wliatever between adults from North Carolina and those 

 from the Bahama Islands, although their life-histories exhibit a most 

 surprising lack of agreement. In fact, the early stages in the life of 

 A. hetcrochelis on the Bahama Islands differ much less from those of 

 A. tninor or A. nor^nani, than they do from those of the North Carolina 

 A. hetcrochelis, and, according to Packard, the Key West hetcrochelis 

 presents still another life-history. 



" The phenomenon is, however, a highly remarkable one, and 

 worthy the most thorough examination, for it is a most surprising 

 departure from one of the established laws of embryology ; the law 

 that the embryonic and larval stages of animals best exhibit their 

 fundamental affinities and general resemblances while their specific 

 characteristics and individual peculiarities make their appearance 

 later." 



