330 Tropical Zoology. (July, 
With regard to the origin of species we extract the fol- 
lowing interesting passage :—‘‘ The great mortality among 
the insects of Chontales, in 1872, has some bearing on the 
origin of species, for in times of such great epidemics we 
may suspect that the gradations that connect extreme forms 
of the same species may become extin¢ét. Darwin has 
shown how very slight differences in the colour of the skin 
and hair are sometimes correlated with great immunity from 
certain diseases, from the action of some vegetable poisons 
and the attacks of certain parasites. Any variety of species 
of insects that could withstand better than others these 
great and probably periodical epidemics would certainly 
obtain a great advantage over those not so protected, and 
thus the survival of one form and the extin¢tion of another 
might be brought about. We see two species of the same 
genus, aS in many insects, differing but little from each 
other, yet quite distinét, and we ask why—if these have 
descended from one parent form—do not the innumerable 
gradations that must have connected them exist also? 
There is but one answer :—We are ignorant what characters 
are of essential value to each species; we do not know why 
white terriers are more subject than darker-coloured ones to 
the attacks of the fatal distemper; why yellow-fleshed 
peaches in America suffer more from diseases than the 
white-fleshed varieties ; why white chickens are most liable 
to the gapes ; or why silkworms which produce white cocoons 
are not attacked by fungus so much as those which produce 
yellow cocoons. Yet in all these cases, and many others, it 
has been shown that immunity from disease is correlated 
with some slight difference in colour or structure; but as to 
the cause of that immunity we are entirely ignorant.” 
In the following passage the author leads up to that phase 
of Darwinism of which the political economists have been 
making use :—‘‘It was this constant struggle between the 
different tribes that weeded out the weak and indolent, and 
preserved the strong and enterprising; just as among many 
of the lower animals the stronger kill off the weaker, and 
the result is the improvement of the race.” 
Many persons in these days talk glibly about the “battle 
of life’? and the ‘‘ survival of the fittest,” and the improve- 
ment of the race. But the question may arise—Who are 
the fittest ? If we look at the vegetable world we find that 
the species precious to us for food, medicine, or clothing, 
and the kinds which delight our senses with the grace of 
their shapes, the beauty of their colours, or the delicacy of 
their odours, are precisely not the forms which would come 
