1 86 ARACHNOIDEA. 



CASE character is their having a small carapace or shield on the back 

 behind the head. Some have eyes, and some none. The habits 

 of the species must at first be herbivorous, for it is from the 

 herbage that they find their way to the creatures on which they 

 fix; but when mature, they greedily avail themselves of -every 

 opportunity of settling on vertebrate animals, whose blood they 

 suck instead of sap. It is a remarkable feature in the economy 

 of these minute animals, that the same species at different stages 

 of its life should thus be at one time phytophagous, and at another 

 carnivorous. The usual special adaptation of structure to kind of 

 food would seem to be absent, but the anomaly is only apparent. 

 Carnivorous mammals are provided with a different apparatus for 

 obtaining their food from that of vegetable feeders ; not no account 

 of the difference in the chemical constituents of their food, but on 

 a-ccount of the different form in which it is presented to them for 

 consumption and assimilation. If, for example, the food of both 

 was presented to them in a liquid state, in the one case blood, 

 and in the other juice of plants, we may be sure that the carni- 

 vorous canines in the one case, and the vegetarian molars in the 

 other, would be alike dispensed with, and both would be furnished 

 with a sucking-up or pumping apparatus, which might be identical, 

 if no speciaHty in the mode in which the liquid presented itself 

 called for a difference. There might be a difference in the 

 structure of their viscera, adapted to the chemical character of the 

 liquid food, but there is no teleological reason why the external 

 and oral structure should not be the same in both. This is what 

 we find in all suctorial insects— bugs, gnats, acari, &c. All are 

 provided with a sucking apparatus, constructed on a similar plan, 

 which some use upon animals, and others upon plants. It has 

 been even said that some, as the bed-bug, feed upon the juice of 

 plants and blood of animals indifferently, and the impossibility of 

 immense swarms of mosquitoes ever tasting foodat-all in the perfect 

 state, if they are restricted to the blood of mammals, has been 

 adduced as an argument in support of their doing so too. It is to 



