AGELENA N^VIA WALCKEN^R 169 



web is at once perceived by the animal. Some of the hair on the 

 appendages is exceptionally fine and erect, sitting in the centre 

 of a small, disc-like or hemispherical membrane. This hair is 

 called trichobothria, and is supposed to convey the impressions of 

 air vibrations or sound. Yet real sense of hearing is wanting 

 in all spiders. An olfactory function has been ascribed to special, 

 so-called lyriform organs appearing as minute slits on the legs 

 near the articulations and elsewhere in the integument. But 

 only strongest odors, such as emitted by essential oils or acetic 

 acid, can be perceived and even these imperfectly. The eyes 

 are fairly well developed. They are situated on the carapace, 

 eight in number, and belong to the type of simple eyes or ocelli. 

 The eyes form two strongly procurved rows and are designated 

 in systematics as anterior middle, anterior lateral, posterior 

 middle, and posterior lateral eyes. But in reality the lateral 

 eyes of the anterior row belong together with the eyes of the 

 posterior row to the first somite, while the anterior median eyes 

 alone belong to the second somite. Moreover, the anterior 

 middle eyes belong to a different type than the other six eyes, 

 inasmuch as they possess a direct retina, while the others have an 

 inverted retina. An ocellus is typically composed of a chitinous 

 corneal lens, a vitreous or glass body and a retina. A ring of pig- 

 ment under the lens serves as an iris. The retina of the inverted 

 eyes is provided with a tapetum behind the rods. The images 

 formed by the eyes are very sharp, but the acuity is very slight, 

 so that the spider is not able to see much detail. 



Reproductive system. The sexes are separate and may be 

 easily recognized. The legs of the male are much longer in pro- 

 portion to its carapace, while the abdomen of the female is con- 

 siderably distended by the growing ovaries. At the same time 

 the modified and enlarged terminal joint of the pedipalpi in the 

 male makes the recognition quite simple. 



(a) Female. Two ovaries occupy almost all the space below 

 the intestine in the abdomen. Each forms anteriorly a short ovi- 

 duct, the two oviducts uniting in a still shorter uterus. The 



