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 

 teachable; 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 

 ada.pt 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 



