of the Amazons Valley. 389 



remarked that they offer some of the best characters to distin- 

 guish species, and they have been made use of to separate species 

 which scarcely offered any other distinguishable characters. 

 Mr. Baly has also discovered that the horny penis concealed in 

 the male abdomen of Phytophagous Coleoptera differs in form 

 in closely allied species ; and he has shown me a long series of 

 specimens mounted for examination under the microscope, be- 

 longing chiefly to the genera Chrysomela and Eumolpus, which 

 offer a most instructive study, since by their means some forms 

 before considered as varieties turn out to be distinct species. 

 This class of facts seems to me of great significance, as throwing 

 light on the segregation of varieties and their passage into true 

 species. For if we admit that the only sound difference between 

 allied varieties and allied species is that the former intermarry, 

 and the latter do not, then the abrupt and great diversities of 

 structure in those organs most directly involved in the matter 

 must be considered as affording an explanation why many varie- 

 ties do not intercross with the parent stock, and therefore re- 

 main as independent forms or species. The difference in the 

 accessory male organs of our two allied species or local forms of 

 Colobothea is so great that no one who examines them can be- 

 lieve both to be adapted to the corresponding organs of the 

 females of each form. At the same time I have no doubt that, 

 were it not for the great difference between these organs in our 

 two forms, no entomologist would doubt their being mere local 

 varieties of one and the same stock. Scores of other local varie- 

 ties occur in the same countries, presenting all the successive 

 steps of segregation, from the most partial variation to the full- 

 formed local race. 



Thus we have only to admit that species disseminate them- 

 selves over wide areas, and adjust themselves to the diversities 

 of local conditions, or, in other words, segregate local varieties, 

 to open the way towards an explanation of the way in which 

 the world has become peopled by its myriads of species. The 

 inevitable law of Natural Selection which governs the general 

 process of the adjustment of the local races to new conditions 

 will explain the changes of conditions of life in time ; and the 

 laws of variation, diversified in details as are the species them- 

 selves, will explain the rest. 



21. Colobothea bisicfnata, n. sp. 



C modice elongata, fusca ; thorace vittis novem cinereis ; elytris 

 maculis parvis subconfluentibus cinereis, relicto spatio medio fusco 

 maculam magnam albam includente. Long. 5 lin. ^ $ . 



Head rusty brown, streaked with ashy, vertex with two ashy 

 lines divergent towards the occiput. Antennae rusty brown, 



