Page:Popular Science Monthly Volume 36.djvu/409

Rh slight flesh tint). But in Bradford Cave, a grotto in Indiana, only three hundred to four hundred yards deep, where the conditions are naturally more variable, the species likewise varied more in proportion of parts, and in respect to the eyes, which were more rudimentary, while the individuals were. whiter.

We have attempted to show that the only known species of the myriapod genus Pseudotremia has been derived from the widely diffused Lysiopetalum lactarium (Say); it differs in having only about half as many segments as in its out-of-door parent form (this diminution in the number of segments being, due to arrest of development); in the smaller, rudimentary eyes, while the antennse are slenderer and longer. Now, in the Carter Caves of eastern Kentucky we found specimens which prove to us that the cave form is only a modified L. lactarium. In those caves Pseudotremia cavernarum is only partly bleached, being brownish; the eyes are larger, having from twenty-three to twenty-five facets; and the general appearance of the specimens is such, especially the prominent ridges on the latero-dorsal tubercles, that the specimens might be mistaken for pale, partly bleached L. lactarium; yet the variety (Carterensis) is true to its generic character, having half as many segments as in Lysiopetalum. Why the number of body segments should be so greatly diminished in the cave form is only explicable on the ground that it is due to an arrest of development, or that the cave form has descended from some unknown species of Lysiopetalum, with half the number of segments as L. lactarium.

In like manner the Mammoth Cave hairy myriapod, Scoterpes Copei, was evidently derived from some species of the hairy genus ''Trichopetalum. Scoterpes has no trace of eyes, and differs from Trichopetalum'' in the longer legs and slightly longer and slenderer antennæ. There is no reasonable doubt but that Scoterpes is a bleached Trichopetalum which has lost its eyes, and consequently has longer legs. Some systematists may yet refer it to Trichopetalum, to which it has the same relations as Anophthalmus to Trechus. It should be observed that several myriapods found in twilight within the mouths of caves, such as species of Polydesmus and Cambala, are more or less bleached, showing the change wrought by a life in partial darkness after a limited number of generations.

The Podurans afford instances of the modification of color especially. Whether living in caves in the central States or in Utah, the common cosmopolitan Tomocerus plumbeus is bleached, retaining its eyes, though they are of diminished size. This is, however, rather a twilight than a true cave species.

The beetles of the genera Anophthalmus and Adelops are the best-known examples of cave animals. The Adelops of Mammoth