For these reasons I think that the fact that the hairless dog of tropical America has not interbred with the common form, and regained its hairy coat, is in favour of the inference that the variety has been produced by natural and not by artificial selection. By this I do not mean that it has arisen as a wild variety, for it is probable that its domestication was an important element amongst the causes that led to its formation, but that it has not been produced by man selecting the individuals to breed from that had the least covering of hairs. I cannot agree with some eminent naturalists that the loss of a hairy covering would always be disadvantageous. My experience in tropical countries has led me to the conclusion that in such parts at least there is one serious drawback to the advantages of having the skin covered with hair. It affords cover for parasitical insects, which, if the skin were naked, might more easily be got rid of. No one who has not lived and moved about amongst the bush of the tropics can appreciate what a torment the different parasitical species of acarus or ticks are. On my first journey in Northern Brazil, I had my legs inflamed and ulcerated from the ankles to the knees from the irritation produced by a minute red tick that is brushed off the low shrubs, and attaches itself to the passer-by. This little insect is called the "Mocoim" by the Brazilians, and is a great torment. It is so minute that except by careful searching it cannot be perceived, and it causes an intolerable itching. If the skin were thickly covered with hair, it would be next to impossible to get rid of it. Through all tropical America, during the dry season, a brown tick (Ixodes bovis), varying in size from a pin's head to a pea, abounds. In Nicaragua, in April, they are very small, and swarm upon the plains, so that the traveller often gets covered with them. They get upon the tips of the leaves and shoots of low shrubs, and stand with their hind-legs stretched out. Each foot has two hooks or claws, and with these it lays hold of any animal brushing past. All large land animals seem subject to their attacks. I have seen them on snakes and iguanas, on many of the large birds, especially on the curassows. They abound on all the large mammals, and on many of the small ones. Sick and weak animals are particularly infested with them, probably because they have not the strength to rub and pick them off, and they must often hasten, if they do not cause their death. The herdsmen, or "vacqueros," keep a ball of soft wax at their houses, which they rub over their skin when they come in from the plains, the small "garrapatos" sticking to it, whilst the larger ones are picked off. How the small ones would be got rid of if the skin had a hairy coat I know not, but the torment of the ticks would certainly be greatly increased.