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THE AMERICAN NATURALIST [Vol.XLVI 



scarcely showing at birth, but developing to a moderate 

 extent rapidly afterward. 



With less favorable conditions the transition is pro- 

 longed and the number of intermediate individuals is 

 greatly increased. I have observed no instance, how- 

 ever, in which the species remained for longer than two 

 weeks in a chaotic condition. Either the transition is 

 soon effected or the numbers rapidly decrease and the 

 species disappears. 



Nearly similar statements may be made with regard to 

 the transition from the humped to the campanulate type. 

 As already stated, its advent usually occurs by the ap- 

 pearance of a very few individuals with the utmost 

 abruptness. Aside from the fact that the ontogeny is 

 here somewhat more extended — they, the young, being 

 considerably smaller than the adults, with much less ex- 

 panded corona— there is apparently little, if any, sense of 

 transition. I think it probable that the humped indi- 

 viduals which actually give rise to the very first campan- 

 ulates are individuals of somewhat extra size and vigor. 

 Such individuals have been found at different times as 

 well as in the case of the two mentioned in my first inves- 

 tigation, but their actual production of the young canni- 

 bals has not been observed. In any case their deviation 

 from the ordinary humped type is not great and the usual 

 transition has all the abruptness that the most pro- 

 nounced mutationist could anticipate. Moreover, as long 

 as the species is thriving and reproduction copious, the 

 two forms remain separated from each other as sharply 

 as do the most distinct species. This is the most fre- 

 quent condition by far in which one finds them. 



"When, however, conditions become less favorable, 

 which fact usually means that the food supply of the 

 humped form is failing, a change intervenes. The 

 humped individuals usually remain quite as they were, 

 without reduction in size or loss of other characteristics, 

 save a much slower rate of reproduction. But this re- 

 duces numbers, and especially the number of young. 



