CXXXlll 



other insect is a Noctuid, Oxyodes scrobiculata, a very common 

 species throughout the Oriental Region, a distribution from 

 Ceylon to New Caledonia being assigned to this moth. The 

 differences in colouring are slight and so unstable that nobody 

 seems to have suspected this 0. scrobiculata to be composed of 

 a number of forms. A study of the structure upsets the 

 notion of uniformity altogether. What we call 0. scrobiculata 

 comprises the following forms : (1) the first figure represents 

 a Ceylonese specimen ; all Ceylonese and South Indian 

 examples are sharply defined by the structure of the tail-ends, 

 and this form extends into North India, where it occurs 

 together with the next one, the differences being such that 

 interbreeding would be interfered with; (2) from North 

 India over Indo-China to Sumatra and Borneo a second form 

 is found; (3) from Palawan and Java to Timor and New 

 Caledonia occurs a somewhat brighter yellow insect with 

 widely different tail-ends, and (4) in Queensland we find again 

 a form structurally similar to the Indo-Malayan one, but 

 different in some detail. There can be no doubt that both in 

 the Geometrid Nobilia and the Noctuid Oxyodes the various 

 forms are modifications derived from the same original stock. 

 Their distribution proves that each form attained its high 

 degree of diversity in an area geographically separate from 

 the countries inhabited by the sister forms. That is to say, 

 geographical segregation has here led to structural segregation 

 and finally to such great diversity that the resulting varieties 

 are as distinct as species. This conclusion based mainly on 

 the morphology of the insects is corroborated by other observa- 

 tions on geographical varieties. It was Standfuss, I think, 

 who first noticed that varieties from the same or similar 

 locality were much easier to cross than geographically separate 

 varieties, the aversion existing between species being already 

 present to some extent in geographical varieties. Moreover, 

 the fertility of such crosses was found to be impaired, and the 

 offspring to be intermediate between the parents, as in the case 

 of crosses between species. Further, according to observations 

 on the fertilisation of the egg-cell and the subsequent fate of 

 the S and ? nuclei, the number of particles into which the 

 nucleus of the fertilised egg breaks up in the process known as 



