192 Report S.A.A. Advancement of Science. 



individuals from the same locality ; in the verreauxii sub-group its 

 size is fairly constant, and an enlargement of that found within the 

 tentoria sub-group ; in oculifera and geometrica it has very fixed and 

 definite characters, being strongly triangular in one, and long and 

 narrow in the other. 



The femoral tubercle illustrates the same conditions. In the 

 tentoria, geometrica, and trifneni sub-groups it may be wl oily want- 

 ing or feebly developed, but in some tentoria it is represented by a 

 large, conical upgrowth, around which the minute body shields begin 

 to enlarge and project in a buttress-like manner. The last-mentioned 

 condition is further exaggerated in the verreauxii sub-group, where 

 the tubercle itseif shows but little plasticity, while the accessory 

 shields are very variable in number and size. In many individuals 

 they altogether encircle the principal spine, while in others they are 

 less in number, and may ultimately be represented by only one 

 much enlarged shield adjacent to the original. In oculifera the 

 principal tubercle is very constant in size, while the surrounding 

 shields are never more than feebly developed. 



The condition of the antebrachial shields throughout the group 

 afi^ords another similar illustration. Within a limited range they are 

 very plastic in all the sub-groups, but in oculifera they exhibit fairly 

 fixed characters. 



Thus, taking almost any character in detail, we find that in 

 some sub-groups it is in a strongly fluctuating condition, in different 

 individuals it is in different stages of development, while in other 

 sub-groups it everywhere presents approximately the same stage or 

 condition. Taken as a whole, the individual characters in the tentoria 

 sub-group are very unstable, and to a less degree this is the case 

 with the verreauxii sub-group, while in octilifera, trimeni, and geo- 

 metrica the variations are much more fixed. As will be shown more 

 fully later, the tentoria and verreauxii sub-groups are to be regarded 

 as transitional in very many ways, while oculifera is an extreme, more 

 permanent sub-group, and, as would be expected, the individual 

 characters are more fluctuating in transitional types than in extreme 

 types. 



The fluctuating condition may be taken as indicative of the 

 activity of the processes of germinal selection, perhaps accompanied 

 by environmental changes, and under isolation would be conducive to 

 the establishment of new types, while the fixed condition is indicative 

 of a cessation of germinal selection, perhaps due to constancy of 

 environment, and is not conducive to the production of new forms. 



c. Introduction of New Characters. 



The discussion of the individual characters has been limited to 

 those which are of diagnostic importance, and which seemed of 

 especial value for the present studv. It is manifest that the work 

 might have been extended by treating in the same manner all the 

 internal structures, though probably with results only of the same 

 kind. With one or two exceptions, all the characters noticed 



