9P THE ANIMAL FRAlViE. 



tanks which are made in India as reservoirs for rain-water : and producing 

 their respective kinds in this situation, have appeared, to the astonishment 

 of all beholders, to have fallen from the clouds with the rain itself. Dr. 

 Thomson, in adverting to this curious fact, observes that it is difficult to 

 account for it satisfactorily.* The explanation now offered will, if I 

 mistake not, sufficiently meet the case. 



Many insects can only be hatched in a particular animal organ ; and it 

 is the office of the integument of the ovum to preserve it in a perfect state 

 till it has an opportunity of reaching its proper nidus. Thus the horse- 

 gadfly, or oestrus equi^ deposites its eggs on the hairs of this animal, and 

 sticks them to the hair-roots by a viscous matter which it secretes for this 

 purpose. But here they could never be hatched, though they were to re- 

 main through the whole life of the horse : their proper nidus is the horse's 

 stomach or intestines, and to this nidus they must be conveyed by some 

 means or other ; and in their first situation they must remain and be pre- 

 served, free from injury and corruption, till they can obtain such a convey- 

 ance. The integument in which they are wrapped up gives them the pro- 

 tection they stand in need of; and the itching which they excite in the 

 horse's skin compels him to lick the itching part with his tongue ; and by 

 this simple contrivance the ova of the gadfly are at once conveyed to his 

 mouth, and pass with the food into the very nidus that is designed for them. 



It is the same integument that, by its incorruptibility, preserves the cater- 

 pillar during the torpitude of its chrysalid state, while suspended by a 

 single thread from the eaves of an incumbent roof ; and which thus ena- 

 bles the worm to become transformed into a butterfly. The larve of the 

 gnat, when approaching the same defenceless state, dives boldly into the 

 water, and is protected by the same indestructible sheath from the dan- 

 gers of an untried element. 



In several species the insect remains in its chrysalid state for many 

 years : the locust, in one of its species at least, the cicada septendecim^ 

 appears in numbers once only in seventeen years, and the palmer-worm 

 once only in thirty years ; cycles not recognised by the meteorologist, but 

 which are well entitled to his attention : and, through the whole range of 

 their duration, it is the integument we are now speaking of that furnishes 

 the animal with a secure protection. 



Whence comes it that plants of distant and opposite climates (for 

 every climate has its indigenous plants as well as its indigenous animals.) 

 should so frequently meet together in the same region ? that those which 

 naturally belong to the Cape of Good Hope should be found wild in New 

 Holland ? . and those of Africa on the coast of Norway ? and that the 

 Floras of every climate under the heavens should consociate in the stoves 

 and gardens of our own country ? it is the imperishable nature of the in- 

 tegument that surrounds their seeds by which this wonder is chiefly ef- 

 fected. Some of these seeds are provided with little hooks, and fasten 

 themselves to the skins of animals, and are thus carried about from place 

 to place ; others adhere by a native glue to the feathers of water-fowls, 

 and are washed off in distant seas ; while a third sort are provided by na- 

 ture with little downy \^ings, and hence rise into the atmosphere, and are 

 blown about by the breeze towards every quarter of the compass. Of 

 this last kind is the light seed of the betula alha^ or birch-tree ; which, in 

 consequence, is occasionally seen germinating oh the summit of the loftif^si 



* Annals of Pliilos. viii. 70. 



