Page:Wood 1865 - The Myriapoda of North America.djvu/19

Rh SCOLOPENDRIDÆ, Leach

Segmenta podophora 21—23. Oculi pauces vel nulli. Pedes postremi incrassati, plerumque spinosi.

Feet-bearing segments 21—23. Ocelli few or none. Last pair of feet thickened and generally spinous.

In this family the principal generic characters are founded upon the number of the segments of the body, the shape of the head, the number and form of the spiracles, the absence or presence of eyes, and the form of the terminal segment and its appendages. In some cases the number of joints of the antennæ seems to be a constant generic sub-character. In the large genus Scolopendra—the Titans of the Myriapoda—the principal specific characters are founded upon, first, the number of segments to the antennæ; secondly, the number and arrangement of the labial teeth; thirdly, the peculiarities of the posterior feet; fourthly, the shape and comparative size of the head. I have no doubt that the number of joints to the antennæ is fixed for most species, but it serves more generally to distinguish groups than single species; yet it occasionally is the most reliable character separating closely allied forms. Unfortunately it must be used with great caution in the identification of individuals; for, owing to the ease with which portions of the antennæ are lost, the want of a certain number is a very indefinite negative character. After detaching a few of the distal joints, no trace of their former presence is left. For the same reason much caution is also necessary in assigning the number in a description. M. Saussure has found so much variation in this character that he considers it worthless. It is possible that it may vary in certain species; but the differences generally consist in there being too few joints, which, as has been just stated, is to be looked for, and reproduced antennæ probably have occasionally an abnormally great number of very small articles. The number and arrangement of the labial teeth sometimes constitute a good character, but there is often an agreement between distinct forms, and on examining large suites of individuals, I have found more variance in the same species than reading would lead one to look for. The posterior legs furnish the best criteria in the distinguishing of species. Most species have peculiarities either in the shape or relative size of the joints, or in the number or arrangement of spines on them. In order to show the amount of constancy that these characters possess, I have drawn up a series of tables, which may aid in establishing their value. The color, I think, is not to be depended upon, although Mr. Newport seems to attach much importance to it. In the preservation of specimens it is very liable to be altered or destroyed; besides this fact, my studies of these animals, both in museums and, to a limited extent, in the Tropics, lead me to the opinion that the color