24 



AMERICAN SPIDEKS AND THEIR SPINNINGWORK. 



sometinies under the ai)ex. This genital plate or lamina corresponds to 

 the apical i)art of the female digital, but the digital claw is entirely 

 wanting, or rudimentary and hidden by i)ubescence. The genital organ is 

 placed under the base of the lamina. It is furnished with processes vary- 

 ing in form, size, and number, and witli a hook or tube (or tubes) which 

 fit into corresponding cavities in the female organ, and transfer the semi- 

 nal Huid tliereto. This peculiar formation does not appear until the last 

 moult, when the s})i(ler is mature. Previous to that the male digital is 

 simply a hairy bulb. The term genital bulb is also a})i)lied to the genital 



organ. Sometimes the bulb is quite one with the lam- 

 ina in which it is muffled, in which case the bulb is 

 called the clava.^ 



During the interval between the third and fourth 

 moulting a considerable change takes place. In the 

 male the extremities of the palpi swell like clubs and 

 develop into different indentations, teeth, threads, or 

 leaves, which later on serve as transmitters of 

 Chane-es ^^^® semen. At first the clubs are filled with 

 semitrans})arent fluid, while the forming inner 

 organs arc yellowish or brownish ; at first the skin is 

 quite soft, but soon hardens and forms a shell, wliich 

 turns darker by the action of the air. Inasmuch as 

 Fig. 13. Leg of Epeira thesc orgaus are almost devoid of soft ])arts it follows 



magnified. Cx, coxa, j. n ii . ^i t m •• 



the joint which unites uaturaliy that as the shell cannot come off, no further 

 the leg with the ster- moultiug cau take place. 



num; tch, trochanter, '^ . ^ 



At the time the pal})i become fully developed a 

 great change takes place also in the female genitals ; 

 the immediate surroundings become roughened and 

 somewhat hardened, presenting little humps which serve 

 partly as rests for the male palpi and partly as recep- 

 tacles for the semen, and is what is designated as " vulva. "'-^ When fully 

 matured the sexes, hitherto separated, come together, and the coi)ulation 

 takes place in a different manner by different varieties.^ 



The legs of the spider are eight, symmetrically disi)osed, four on each 

 side of the sternum to which they are articulated. Their relative lengths 

 give one of the best characters for systematic arrangement. They 

 are numlxTcd from the face backward as first (1), second (2), 

 <'ii''«l '•*'), ••'lid fourlii (1) ]);iii-s.' (Fig. 11.) Tlie relative lengths 

 aiv indicated by a formula composed of the above luimerals arranged in 

 the order of greatest lengths fiom highest to lowest, thus: 12 4 8 is the 

 formula which expresses the prevailing order among Orbweavers and de- 



sman joint by which 

 the femur articulates 

 upon the coxa ; fm, fe- 

 mur ; ptl, patella ; tb, 

 tibia ; mt, metatarsus ; 

 t, tarsus ; cl, claws. 



The 

 Legs 



' VVt-Htriiif,', Arant'a; Svcciti', pn-^M' 12. 



^ MciiL'-c. " |)ic I'rciissisclic Siiiiiiicii." 



^ 8ec' C'luipU^r on " Wooiii^r aiid Matiii'.i lliiMls 



Vol. 11. 



