ADDRESS. 



Ixxiii 



diate between A and Z. A and E on the one hand, and Y and Z on the 



other, might reproduce ; but to regain the original tj'pe M, we must not only 

 retrooede 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 inter- 

 mediate 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 elabo- 

 rate and careful investigations of Dr. Carpenter on Foraminifera, he states, 

 " It has been shown that a very wide range of variation exists among Orbito- 

 lites, 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 

 Avith respect to the size and configuration of its component parts. It Avould 

 have been easy, by selecting only the most divergent types from amongst the 

 whole series of specimens which 1 have examined, to prefer an apparently 

 substantial claim on behalf of these to bo accounted as so manj- distinct 

 species. But after hanng classified the specimens which could bo arranged 

 around these types, a large proportion would yet have remained, cither pre- 

 senting characters intermediate between those of two or more of them, or 

 actually combining those characters in different parts of their fabric ; thus 

 showing that no lines of demarcation can be drawn across any part of the 

 scries that shall definitely separate it into any number of groups, each cha- 

 racterized by features entirely peculiar to itself." 

 At the conclusion of his inquiry he states, — • 



I. The range of variation is so great among Foraminifera as to include not 

 merely the differential characters \\hich system atists proceeding upon the 

 ordinary methods have accovmlcd specific, but also those upon which the 

 greater part of the genera of this group have been founded, and even in some 

 instances those of its orders. 



II. The ordinary notion of species as assemblages of individuals marked 

 out from each other by definite characters that have been genetically trans- 

 mitted from original proto-types similarly distinguished, is quite inapplicable 

 to this groTip ; since even if the limits of such assemblages were extended so 

 as to include what elsewhere would be accounted genera, they would still be 

 found so intimately connected by gradational links, that definite lines could 

 not be drawn between them. 



III. The only natural classification of the vast aggregate of diversified 

 forms which this group contains will be one which ranges them according to 

 their direction and degree of divergence from a small number of principal 

 family tj^^es; and any subordinate grouping of genera and species which 

 may be adopted for the convenience of clesciiption and nomenclature must 

 be regarded merely as assemblages of forms characterized by the nature and 

 degree of the modifications of the original type, which they may have respec- 

 tively acquired in the course of genetic descent from a common ancestry. 



IV. Even in regard to these family types it may fairly be questioned 

 whether analogical evidence does not rather favour the idea of their deriva- 

 tion from a common original than that of their primitive distinctness. 



Mr. H. Bates, when investigating " The Lepidoptera of the Amazon Valley ," 

 may almost be said to have witnessed the origin of some species of Butterflies, 

 so close have been his observations on the habits of these animals that have 

 led to their variation and segregation, so closely do the residts follow his 

 observations, and so great is the difficulty of otherwise accounting for any 

 of the observed facts. 



