30 'J^'y- 



the mango, rarely or never settle, and about 3 p.m. begin to come up 

 the stream, when they gradually disaj)pear. Every one 1 secured was 

 captured on the wing. I never saw them alight on flowei'S ; but, on 

 two occasions, I saw one settle on the top of a mango tree. Its mode 

 of flight is very deceptive, appearing to be slow, but, in reality, is very 

 rapid. It is fearless, if one remains perfectly quiet, but the slightest 

 movement will cause it to swerve in its flight. I tried very hard to 

 discover the caterpillar, and offered rewards to the natives for it, but 

 my efforts were fruitless." 



The extraordinary fact of such a large and strongly winged but- 

 terfly capable, one would think, of long and sustained flight from one 

 region to another, being confined to such a small area as that comprised 

 by Jamaica, is highly significant, in view of some of the problems 

 raised by the subject of the geographical distribution of species. The 

 large majority of Lepidojytera, we know, are dependant for their 

 range of distribution upon that of the plants upon which their cater- 

 pillars feed ; and while, in the case of a widely distributed species, we 

 argue either a corresponding extension of its food plant, or a capability 

 of adapting itself to more than one kind of plant, we naturally infer, 

 when we find another species confined to a small area, that it is so 

 restricted because its food plant does not extend beyond the same 

 region. It is a well known fact, that many of the older foi-ms of plant 

 life, unable to adapt themselves to recent climatic changes, have gra- 

 dually narrowed their range of distribution, and already show signs of 

 becoming extinct. If we suppose the case of a plant at one time 

 distributed over a large area, and furnishing food for a given species 

 of butterfly, gradually yielding to adverse influences until it becomes 

 confined to one locality in which alone it found the conditions favour- 

 able to its existence, the butterfly, unless it had been able to find food 

 elsewhere, would suffer a corresponding restriction and diminution in 

 numbers until it at last quite died out. This would be pre-eminently 

 the case with such species as originated during a period when the 

 physical conditions of a given region were different from what they 

 are at present. I am inclined to regard P. Somerus as an illustration 

 of this general law, and feel convinced that when its food plant is 

 known, it will prove to be not only one of the rarest but also one of 

 the oldest forms of the flora of the "West Indies. In the extract given 

 above, the mango is mentioned as one of the plants to which P. Ho- 

 merus shows a preference, and it may occur to some that this may be 

 the food plant of the species. This, however, is hardly probable, as 

 the m.TUgo ha? bepn introduced into Jamaica only within very recent 



