54 



inexperienced observer, although none of the great Class to which 

 the Mites belong have any antennas at all, is yet very apt to consider 

 the front pair of legs as antennae, whenever he sees them used as 

 antennas. Consequently, as a general rule, the easiest mode for be- 

 ginners to distinguish a Mite from a true Insect is, to see whether 

 the animal under examiuation has a distinct head or not. If it has, 

 it cannot be a Mite. If it has not, it cannot be a true Insect. 



So far we have been talking about the structural peculiarities of 

 the perfect Mite and the perfect Insect. In the larva or imperfect 

 stale the case is somewhat different. Just as, in the larva state, 

 many Insects have legs so minute that they are scarcely distinguish- 

 able, others again have no legs at all, others again, in addition to the 

 six normal jointed legs, have at their tails a sham leg (or "pro-leg") 

 or fleshy excrescence not divided into joints like the true legs, but 

 still performing the same functions as they do, and others again have 

 from four to sixteen of such sham legs strung along the hinder part 

 of their bodies, besides having the normal six true legs in front; so, 

 in the larva state, many Mites have only six legs, although, when 

 fully grown, they acquire an additional pair. In this case, as these 

 Mite-larvae are always exceedingly minute in size, it is sometimes 

 not very easy to distinguish them from the similarly minute larvae of 

 certain Bark-lice and Plant-lice, to which they bear a strong general 

 resemblance. There is, however, one distinctive character by which, 

 so far as a pretty extensive observation goes, I believe that the very 

 young six-legged oval larvae of the Mites may be always readily dis- 

 tinguished from the very young six-legged oval larvae of the Bark-lice 

 and the Plant-lice. In the two latter groups the three pairs of legs 

 are always equidistant, or nearly so, from each other, at their origin 

 on the lower surface of the body. In the former group the two front 

 pairs of legs are placed close to one another on the lower surface of 

 the body and not very far from the front end, while the hind pair of 

 legs are placed wide apart from the others and not very far from the 

 hind end. In a somewhat' wide experience with these creatures, I 

 have met with no intermediate grades whatever in these very remark- 

 able characters. 



Of course, as the larvae of all Bark-lice and Plant-lice have an- 

 tennas, and those of Mites have none, if you can make out the anten- 

 nae clearly in the larvae that you have under examination, 

 they cannot be Mite-larvae. But as the larvse of Bark-lice 

 and Plant-lice very frequently do not raise up their antennae as 

 they crawl along, and as the legs can generally be made out pretty 



