What the use of this phosphorescence may be is not known with any degree of certainty. It may be either a defence against enemies, or else a means of attracting the two sexes to one another. The places which the Myriapods select for their habitation vary as much as their colour and size, though, with a few exceptions, they chose dark and obscure places. A curious species of Myriapod is _Pseudotremia cavernarum_ (Cope), which is found in certain caves in America. The peculiar life it leads in these caves seems to have a great influence on its colour, and also affects the development of its eyes. Mr. Packard's account of them is worth quoting: "Four specimens which I collected in Little Wyandotte cave were exactly the same size as those from Great Wyandotte cave. They were white tinged, dusky on the head and fore part of the body. The eyes are black and the eye-patch of the same size and shape, while the antennae are the same. "Six specimens from Bradford cave, Ind. (which is a small grotto formed by a vertical fissure in the rock, and only 300 to 400 yards deep), showed more variation than those from the two Wyandotte caves. They are of the same size and form, but slightly longer and a little slenderer.... The antennae are much whiter than in those from the Wyandotte caves, and the {35}head and body are paler, more bleached out than most of the Wyandotte specimens.... It thus appears that the body is most bleached and the eyes the most rudimentary in the Bradford cave, the smallest and most accessible, and in which consequently there is the most variation in surroundings, temperature, access of light and changed condition of air. Under such circumstances as these we should naturally expect the most variation."[12] A strong contrast to these animals is afforded us by the Scutigeridae (Schizotarsia). They are unknown in this country, but abound in some of the Mediterranean countries and in parts of Africa. They remind one strongly of spiders, with their long legs and their peculiar way of running on stones and about the walls of houses. [Illustration: FIG. 17.—_Cermatia (Scutigera) variegata._ (From C. L. Koch, _Die Myriapoden_.)]