CHAPTER OF VARIETIES. 155 



stance of my writing in London which led to this mistake, which I hope 

 you will excuse, being from a tyro. I am aware that in country villages 

 the robins are plentiful throughout the year, though when the young, 

 have flown, like all other birds, they are most abundant ; and yet the 

 next breeding season they do not appear more so than the last, and we 

 never notice, in any district, one species to become gradually more 

 numerous. As, for instance, the swallow: the departing flocks are beyond 

 comparison larger than those which return in spring, and one would 

 suppose that there would be a perceptible increase, but this is checked 

 by numerous accidents, to which migratory birds are subject, such as 

 diminution by storms in crossing the ocean, and by the attacks of birds 

 of prey and other enemies in travelling overland : so admirably is every 

 thing in nature arranged, and so true is the balance of Nature's scales. 



With regard to " animals swallowing hard substances," I had often 

 heard of the ostrich swallowing stones, &c. ; but was surprised to observe 

 the cassowary at the Surrey Zoological Gardens swallowing several 

 stones of considerable magnitude, after having already passed through the 

 bird, apparently without being injured; how often this process was 

 repeated, I had not patience nor inclination to discover ; nor do I know 

 whether it be a new fact respecting this bird or not. T. C. 



Spontaneous generation. — " Tyro" notices animalcules found in 

 water, and says " there can be no doubt, I think, that they owe their 

 being to decomposition." I wish I could give him " a few hints upon 

 this subject ; " but unfortunately can only suggest one or two queries, 

 being more fond of contemplating Nature's more beautiful, though 

 perhaps less astonishing, works. 



1. Do not these animalcules, or at any rate the spawn, eggs, (or 

 from whatever else they may be produced), exist at all times in water ? 

 and is it not their extreme diminutiveness which prevents their being 

 seen, even with a microscope ? 



2. Is it not their increasing in size which renders the water putrid? 



3. Is not decomposition the effect of these very animalcules ? 



I should be glad to be enlightened respecting these points, or infor- 

 med of the best work upon the subject *. T. C. - 



Rats and guinea pigs. — Some people, I believe, have an idea that 

 rats are afraid of guinea pigs ; when I kept rabbits I had great diffi- 



* I have taken up this question at some length in " Insect Transformation." 

 I have also given the more recent discoveries in the " Alphabet of Natural 

 Theology," now in the press. Ed. 



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