Page:Wood 1865 - The Myriapoda of North America.djvu/20

Rh varies exceedingly, even during life. Size is often a good distinguishing character of a species, although scarcely available for the identification of an individual.

If we consider a species as the expression of a preconceived idea, there must be, as it were, a type of every species around which the individuals cluster, restrained from departing beyond a certain limit from the central nucleus. We can see then how there may be species perfectly distinct, but the individuals of which may so approximate that there may be difficulty in placing some of them. Does the mere difficulty or impossibility of placing an individual necessarily invalidate the claims of the species? The moss Leucobryum glaucum, Hampe, is acknowledged by all botanists (I believe) as distinct from L. minus, Hampe, the most tangible difference being that the former fruits in October, the latter in May. Now I have found fruiting specimens in April, which are undoubtedly referable to L. glaucum; but had they been found a month or two later, would any botanist have hesitated in labelling them L. minus? Indeed, one of the best American authorities told me, that had I so found the specimen, he would have pronounced it to be L. minus, as it would not have been possible to have known that the capsules were those of the previous year.

In the other genera of the Scolopendridæ the specific characters are pretty much the same as in the true Scolopendra. But some characters specific in the latter, elsewhere become generic subcharacters.

SCOLOPENDRINÆ, Newport "Spiracula valvularia in paribus 9."

Spiracles valvular in 9 pairs.

SCOLOPENDRA, Linn,

Segmentum cephalicum imbricatum. Oculi stemmatosi, utrinque 4. Antennæ attenuatæ. Pedum paria 21.

Cephalic segment imbricate. Ocelli stemmatous, 4 on each side. Antennæ attenuate. Pairs of feet 21.