332 CAPT. r. W. HUTTON ON THE PROBLEM OP UTILITY. 



legs give one insect an advantage over another ? Again, can we 

 suppose the slight differences in the number or shape of the 

 teeth in the species of Helices, or whether they have ten or 

 twenty ribs to the tentb of an inch on their shells, have any 

 adaptive value ? Tet they are often good and constant specific 

 characters. Or take the shape of the spicules in tbe Holo- 

 thurians or in the Sponges ; or the skeleton in the Eadiolarians, 

 or the small differences in the leaves of ferns and mosses ; or 

 the various ornamentation on the frustules of Diatoms : can 

 all or any of these characters — which are certainly as stable 

 as specific characters whicb are acknowledged to be useful — 

 can any of them be explained by the principle of utility ? If 

 such is the case, wbicb, among two or more species living 

 together, is the best adapted to the conditions, and whicb the 

 worst ? And why has not the worst died out ? Take, for 

 example, the different colours and shapes of the shells of 

 Mussels {Mytilus), two or more species of which often live 

 together under exactly the same conditions : if one colour or 

 shape is more advantageous than the others, why are the others 

 there? "We cannot plead want of time; for many of these 

 species date back to the Pliocene period. Suggestions that it 

 might be this, or it might be that, have no weight with me when 

 I find that the effects which ought to have been produced, if these 

 suggestions were correct, have not been produced : when, for 

 instance, I find that the two species which are compared are 

 equally numerous. 



I could give numerous cases in detail if I thought it necessary ; 

 but, no doubt, every naturalist who has done systematic work on 

 species could furnish them by the score. So I will restrict 

 myself to one example drawn from a class of facts different from 

 those which I have already mentioned. 



There is a genus of small Fruit-Pigeons, called Ptilopus, found 

 from the Malay Peninsula through the Malay Archipelago to 

 Australia and Polynesia. It is a large and dominant genus, divided 

 into twelve sections. One of these sections — Ptilopus (restricted) 

 — contains twenty-three species, of which no fewer than thirteen * 



* P. pelewensis, in the Pelew Islands ; P. roseicapiUus, in the Ladrones ; 

 P. ponapensis, in Euet Island, Caroline Group ; P. Hernsheimi, in Kushai, 

 Caroline Group ; P. Richardsi, in Ugi, Solomon Group ; P. Greyi, in New 

 Caledonia and the New Hebrides ; P. rarofongensis, in Earotonga, Cook's 

 Group ; P. purpurattis, in Tahiti, Society Islands ; P. chrysogaster, in Huahine 



