292 AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



to the gradual progress of the atrophy, or to one of those natural freaks 

 which occasionally occur with spiders as well as other living things. 



Occasional irregularities in the number of eyes are not wholly due to 

 causes which produce the atrophy of those organs. For example, Black- 

 wall l records that an adult female Epeira inclinata captured in August 

 was entirely destitute of the left intermediate eye of the posterior row, 

 and the right intermediate eye of the same row was not the usual size. 

 In another adult female taken in the autumn of the same year the right 

 intermediate eye of the posterior ro\v had not one-eighth of the usual size, 

 being merely rudimentary. This spider abounds in many parts of Great 

 Britain and Ireland, and seems to prefer districts which are well wooded, 

 but otherwise has no habits which would account for such irregularities. 

 It is simply an abnormal state of the eyes, resulting from some morbid 

 condition. 



Concerning Linyphia inserta, drawings of whose eyes are shown at Figs. 

 284 and 285, Emerton says that the eyes are small and colorless and sep- 

 arated from each other. The front middle pair are very small, hardly 

 larger than the circles around the base of the hair by which they are sur- 

 rounded, and only distinguished from them by wanting the dark ring 

 which surrounds the hair circles. In five females from Fountain Cave all 

 the eyes are present. (Fig. 285.) In one female one eye of the front mid- 

 dle pair is wanting. In three males from the same cave both front middle 

 eyes are wanting, as in Fig. 284. In one male only one of the front mid- 

 dle pair is wanting. In four females and one male from Bat Cave, Carter 

 County, Kentucky, the front middle eyes are wanting. 2 This irregularity 

 in the number of the eyes indicates with little doubt the fact that the in- 

 fluence of environment has been strongly felt in producing a greater or less 

 atrophy of these organs of sight. 



IV. 



That spiders have accurate perception of the direction and intensity of 

 light, one may easily determine by experiments with the young. A great 

 number of such experiments I have made, but will content myself with 

 an illustration or two which fully typify the universal tendency. A brood 

 of young Zillas heretofore described (Volume I., page 143) habitually 

 placed themselves upon the illuminated side of their common 

 to Light we k- ^is position during the day looked toward a bay win- 

 dow a few feet from the table on which the colony was settled, 

 and at night was on the opposite side and toward the lamp on my desk. 

 In the morning, if the day were bright so that the sunlight streamed in 

 at the bay window, the colony invariably migrated to that side. If the 

 day were dull, inasmuch as a side window shed some light over the table, 



1 Spiders Gt. Bt. & Ir., page 355. 2 Op. cit., page 280. 



