132 SYMBIOGENESIS 



occupied a time vastly greater than that of which we have a 

 record, for which view, he says, we have no more than an 

 antecedent probability. He suggests that habits may have 

 something to do with relative slowness or quickness of evolu- 

 tion. The species of the pre-Cambrian era had perhaps not yet 

 acquired the "lime-habit," i.e., as I would say, surfeiting 

 nutritional habits. If so, they could accomplish more evolu- 

 tion in comparatively shorter time than subsequent assemblages 

 of animals which, in connection with their surfeiting habits, 

 had made the fatal adaptation of forming heavy carapaces ; 

 and we are not warranted in making the slowness of evolution 

 during the latter phase a measure of the time it must have' 

 taken evolution to raise the unencumbered antecedent species. 

 We may be dealing with different orders of facts. 



" It will be generally admitted that the formation of 

 exterior protective lime coatings is likely to render further 

 developments both difficult and unnecessary." 



"The one notable example of the higher development of 

 such invertebrate forms, the Cephalopods, has only taken place 

 as and when the protective coating has obsolesced." 



In the course of his argument, showing that there is 

 frequently little validity in the geological arguments as used 

 by biologists, the same writer touches on the problems of " use- 

 inheritance " and Mendelian laws of inheritance. He states 

 that as regards the higher animals it is now generally 

 recognised that the mutual infertility of nearly allied species 

 is a test of species difference, and, further, "Physiological 

 infertility is evidently not correlated with accidental 

 differences in shape, colour or form, but connotes an essential, 

 deep-seated organic change." 



Again, we thus see how everything points to a deep-seated 

 qualitative change, i.e., to a change of bio-economic (and 

 associated physiological and bio-chemical) value as a necessary 

 preliminary to or concurrently with the formation of new species. 



"It seems probable, therefore," continues Mr. Shelton, 

 "that this mutual infertility may not be obtainable by 



