cxciv GENERAL SUMMARY OF SCIENTIFIC AND 



that it is due to an imperfect fecundation of the ovum seems 

 most probable. Thdse cases seem to be paralleled by the oc- 

 currence of hybridity between two species, the result being 

 an irregular fusion of the characters of both species. Both 

 seem to indicate that sexual characters, as well as specific 

 characters, are determined at the time of impregnation. 



Mr. Scudder's discovery of well-preserved remains of the 

 abdomen of a larval dragon-fly in the coal-measures of Cape 

 Breton sets back a long ways the existence of these insects, 

 the earliest remains heretofore known having occurred in the 

 Lias formation. 



As a contribution to fossil entomology, the splendid mem- 

 oir of Mr. Scudder on fossil butterflies is noteworthy. Nine 

 well-authenticated species of fossil butterflies are now known, 

 all from the European tertiary formation, the earliest known 

 forms occurring in the lower beds. Three of these insects be- 

 long to the highest families of butterflies Nymphales four 

 to the Papilionidae, and two only to the Urbicola3 (Hesperi- 

 aus). The allies of four of these fossil butterflies now live 

 in the East Indies ; those of three in sub-tropical North 

 America, and one of them in the north temperate zone of 

 both Europe, Asia and America; and those of one in the 

 Mediterranean region. Three out of the four species whose 

 living allies are to be sought in the East Indies come from 

 the older deposits of Aix, and only one of the two remain- 

 ing Aix species shows special affinities to American types ; 

 " We thus find here, as among other insects and among the 

 plants, a growing likeness to American types as we pass up- 

 ward through the European tertiaries. 



" The study of the floras of the European tertiaries has 

 proceeded so far that in most cases we are able to find, in 

 the very beds where the butterflies occur, plants which we 

 may reasonably judge to have formed the food of these in- 

 sects in their earlier stages. In but a single instance is the 

 family of plants upon which it was necessary, or almost 

 necessary, to suppose the caterpillar fed, entirely absent 

 from tertiary strata ; and since this family is the Cruciferae, 

 which in its very nature could scarcely have left a recogniz- 

 able trace of its presence, the exception has no force." 



Professor Weismann's work on "Seasonal Dimorphism" 

 in butterflies shows that several so-called species are simply 



