CONTINUITY. 215 



offspring by successive changes through eons of time have 

 divaricated, and running opposite ways which we may denote 

 by the letters of the alphabet, have produced on the one hand a 

 species A, and on the other a species z : the changes here have 

 been so great that we should never expect directly to reproduce 

 an intermediate between A and z. A and B on the one hand, 

 and Y and z on the other, might reproduce ; but to regain the 

 original type M, we must not only retrocede through all the 

 intermediates, but must have similar circumstances recalled in 

 an inverse order at each phase of retrogression, conditions 

 which it is obviously impossible to fulfil. But though among 

 the higher forms of organic structure we cannot retrace the 

 effects of time and reproduce intermediate types, yet among 

 some of the lower forms we find it difficult to assign any line 

 of specific demarcation ; thus, as a result of the very elaborate 

 and careful investigations of Dr. Carpenter on Foraminifera, 

 he states : ' It has been shown that a very wide range of varia- 

 tion exists among Orbitolites, not merely as regards external 

 form, but also as to plan of development ; and not merely as 

 to the shape and aspect of the entire organism, but also with 

 respect to the size and configuration of its component parts. 

 It would have been easy, by selecting only the most divergent 

 types from amongst the whole series of specimens which I 

 have examined, to prefer an apparently substantial claim on 

 behalf of these to be accounted as so many distinct species. 

 But after having classified the specimens which could be 

 arranged around these types, a large proportion would yet 

 have remained, either presenting characters intermediate 

 between those of two or more of them, or actually combining 

 those characters in different parts of their fabric' ; thus show- 

 ing that no lines of demarcation can be drawn across any part 

 of the series that shall definitely separate it into any number 

 of groups, each characterised by features entirely peculiar to 

 itself.' 



At the conclusion of his enquiry he states 



I. The range of variation is so great among Foraminifera 



as to include not merely the differential characters which sys- 



tematists proceeding upon the ordinary methods have accounted 



specific, but also those upon which the greater part of the 



