1908.] NATURAL SCIENCES OF PHILADELPHIA. 159 



most of the small and excessively active Pardosas keep close to the 

 water, when alarmed running out freely over the surface, in 

 adaptation to which action their tarsi are specially modified in the 

 arrangement of hairs and bristles. The larger Lycosas may mingle 

 their colors with those of the dried leaves and twigs of the woods, 

 lurk beneath the stones of roadside and field, wander in the open or 

 burrow in the sand of the seashore or the soil of the plain. Every- 

 where they are familiar; not because of large number of species, nor 

 because of their bold open habits, but especially because of the 

 excessive abundance of individuals resulting from successful adapta- 

 tion to conditions widely available. 



All true spiders depend upon living animals, mostly insects, for food. 

 Since they ingest only the body juices of their prey, what seems at 

 first an amazing quantity of insects is required to satisfy their nutritive 

 needs. Most spiders have met this requirement through the develop- 

 ment of instinct and skill, accompanied of course by those structural 

 modifications necessary for their effective exercise, in the construction 

 of webs. The line of divergence of the Lycosidce, however, has been in 

 the direction of capacity for taking prey by the chase. The high arched 

 cephalothorax and the long stout legs plainly bespeak strength and 

 speed. But strength and speed alone would be quite ineffective 

 without the simultaneous development of the sensory system, to enable 

 the spiders to detect and with some certainty to follow their prey. 

 Such development has affected strongly the sight; other senses, except- 

 ing touch, being seemingly but feebly developed. This is manifest in 

 the differentiations in size and arrangement of the eyes. It has been 

 shown that the arrangement of the eyes is such as to make the animal 

 aware of movements within its limit of vision in front, at the sides 

 and through a considerable arc behind, the arc directly forward being 

 covered particularly well. The eyes fall very clearly in three rows. 

 The first row, situated across the lower part of the face, is composed of 

 four small eyes placed in different planes; the second of two eyes, large 

 in size and directed antero-laterally ; the third of two medium-sized 

 eyes situated farther back on the pars cephalica and directed latero- 

 caudally. This arrangement of the eyes is apparently associated 

 with the characteristic elevation of the pars cephalica. The high 

 dorsally narrowed cephalothorax and the placement of the eyes m 

 three distinct rows as described are features by which the Lycosidce 

 are usually to be detected at a glance. Other characters serving with 

 those mentioned to distinguish members of this family are the three 

 claws of the tarsi, the notching of the trochanters at the outer end 



