GENERAL CLASSIFICATION AND STllUCTUKE. 



21 



Thus Fig. 8 represents the eyes of an Epeira, and Fig. 9 the eyes of the 

 Retitelarian genus Theridium. Dr. Bertkau distinguishes these two tribes 

 by tlie presence in the Epc'iioids of what he calls a basal spot (Basaltieckj 

 upon the mandibles. 



III. 



For the convenience of readers not acquainted with the anatomy of 

 spiders, a general description of the animal is here given. It is not in 

 ^ ;viR accord with the })urpose of this work to enter into the 

 -SR details of ^structure ; for these the studies of anatomists 

 .gr. and liistologists must be consulted. But some knowledge 

 of the })rincipal organs, especially in their relations to 

 the spinning industry, is necessary to the understanding 

 ^ of much of what follows. 



The ])rincipal parts are the cephalothorax and abdo- 

 men. The cephalothorax consists of the cephalic part 

 *§ (cp. Fig. 11) and the thoracic part, tp ; the two parts 



Fig. 8. Face of Epeira. .^y^ uuitcd dircctly, aud uot by a neck, the caput being 

 set innuediatcly upon the thorax, whence the name cephalothorax. The 

 point of juncture is marked by a suture, more or less distinct, extending 

 along the lower margin of the cai)ut backward, on eacli side, and con- 

 verging in a depression more or less profound at the summit of the 

 thoracic part. The cephalothorax is externally a hard, ehitinous case 

 com])()Scd of two principal plates, resendjling more nearly than any other 

 l)art of the body the tough shell of true insects. 



The front and up})er portion of the cephalic part is the cai)ut, which 

 in Orbweavers is sometimes depressed, more frequently elevated. On the 

 fore part of the ca})ut are situated eyes, which in 

 this group are eight, but in other groups sometimes 

 nmnber six and even two. The arrangement of the 

 eyes upon the caput forms good generic and specific characters. 

 The eyes in the Orbweavers are disposed across the caput in 

 two rows of four each, known as front and rear rows (Fig. 8); 

 they are again dividc<l into three groups, of which 

 the middle groui) contains four eyes, known as the fig. 9. Face of 



L i n 6 w G Ji V G r 



middle eyes, those in front being mid front or middle Theridium tc- 

 Iront (M.F.) and those behin<l, the mid rear or middle rear pidariorum. 

 eyes (M.R.). The remaining four eyes, known as the side eyes (or lateral 

 eyes), are placed in two's on cither side of and equidistant from the middle 

 grou]). They are known as the side front (S.F.) and side rear (S.R.) ; they 

 are generally quite near to i^aeh other, frecpiently touch, but occasionally 

 are well separated; foi' the most part they are smaller tlian the middle 

 eyes. They, as well :is the middle grouj), are ui'ten i)laced ui)on tubercles 

 more or less prominent. 



The 

 Caput 



The 



Eyes 



