152 The Naturalist in La Plata. 
of an ant, assuming that this insect possesses a very 
high intelligence, but I doubt very much that the ant, 
which moves in a groove, is mentally the superior 
of the unsocial flea. The last is certainly the most 
teachabie; and if fleas were generally domesticated 
and made pets of, probably there would be as many 
stories about their marvellous intelligence and 
fidelity to man as we now hear about our over- 
praised “friend”’ the dog. 
With regard to size, the flea probably started on 
its downward course as a comparatively large insect, 
probably larger than the Ornithomyia. That insect 
has been able to maintain its existence, without 
dwindling like the Leptus into a mere speck, through 
the great modification in organs and instinct, which 
adapt it so beautifully to the feathery element in 
which it moves. The bush-tick, wingless from the 
beginning, and diverging in another direction, has 
probably been greatly increased in size by its para- 
sitical habit ; this seems proven by the fact, that as 
long as it is parasitical on nothing it remains small, 
but when able to fasten itself to an animal it rapidly 
developes to a great size. Again, the big globe of 
its abdomen is coriaceous and elastic, and is pro- 
bably as devoid of sensation as a ball of india-rubber. 
The insect, being made fast by hooks and teeth to its 
victim, all efforts to remove it only increase the 
pain it causes; and animals that know it well do 
not attempt to rub, scratch, or bite it off, there- 
fore the great size and the conspicuous colour of 
the tick are positive advantages to it. The flea, 
without the subtlety and highly-specialized organs 
of the Ornithomyia, or the stick-fast powers and 
