INTRODUCTION. XV 
the atmospheric and climatic conditions of that country. For organisms of such 
delicate construction, the hygrometric equilibrium of which is so easily disturbed, 
the extreme aridity of the “ verano” or dry season, which in Western Guatemala lasts 
for several months, must prove much more fatal than does even the European winter with 
its frozen and snow-covered ground. On the other hand, the torrential ‘ aguaceros ” 
of the “‘invierno” or rainy season probably cause the destruction of numerous non- 
parasitic soft-bodied and unprotected Acari. It is for these reasons probably that we 
find the greatest variety of species in those genera which are protected to some extent 
by their entirely or partially parasitic habits, such as the Ixodide, Gamaside, Hydrach- 
nide, and Dermaleichide, or which, like Trombidiwm, are capable of a somewhat rapid 
locomotion, which enables them to reach, in case of need, a shelter to protect them 
from being drowned or dried up. The various stages of the tough-skinned ‘“‘ Garra- 
patas” (ticks) are enabled, however, to withstand alike the heat and dryness of the 
‘“‘ verano” and the deluges of the “invierno.” 
The limited number of species is, in some instances at least, counterbalanced to a 
certain extent by an abundance of individuals. This is the case in some species 
which are more resistant, or better protected against the influences of the climate, than 
the majority of their congeners—for example, with Trombidium muricola, Tetrany- 
chus guatemale-nove, Atax alticola, Amblyomma miatum, Orihata centro-americana, 
Holostaspis marginatus, and the various species of Dermaleichide. 
I regret that I had not sufficient opportunities for observing the vertical distribution 
of the Central-American Acarids. My ascents of the volcanos Agua and Fuego were 
both made in the dry season, in the unfavourable months of January and February, 
when, at night, the temperature on the summits was as low as — 2° C., and when, from 
cold and aridity, Arthropod life was reduced to a few species of Insects, Myriopods, 
and Spiders, these living under the bark of the scattered fir trees and under stones *. 
But, judging from what I have observed in the Swiss Alps, where I found a small 
number of such conspicuous types as Rhyncholophus, Erythreus, Oribata, and Gamasus 
* When I passed the night in the crater of the Volcan de Agua, 19/20 February, 1881, I found in the 
morning the water in our jar covered with a crust of ice, Under the bark of a fir tree near the edge of the 
crater I found the dead body of a small species of venomous snake, which had evidently been killed by the 
cold. Notwithstanding, I discovered under a flat stone in the crater itself an ants’ nest, the inhabitants of 
which were winged. This species has since been described by my friend, Prof. A. Forel, as Leptothorax 
stolli. 
