24 AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



4 - Cl 



tr 



sometimes under the apex. This genital plate or lamina corresponds to 

 the apical part of the female digital, but the digital claw is entirely 

 wanting, or rudimentary and hidden by pubescence. The genital organ is 

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

 ing in form, size, and number, and w r ith a hook or tube (or tubes) which 

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

 nal fluid thereto. This peculiar formation does not appear until the last 

 moult, when the spider is mature. Previous to that the male digital is 

 simply a hairy bulb. The term genital bulb is also applied 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. 1 



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 

 Chancres ^ e semen. At first the clubs are filled with 

 semitransparent fluid, while the forming inner 

 organs are yellowish or brow r nish ; at first the skin is 

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

 turns darker by the action of the air. Inasmuch as 

 FIG. 13. Leg of Epeira these organs are almost devoid of soft parts it follows 



magnified. Cx, coxa, 11,1 ,-, i n <v- P ,1 



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

 the leg with the ster- mou lting can take place. 



num; ten, trochanter, . A 



smaii joint by which At the time the palpi become fully developed a 



Ipl^coxaffmrS S reat chan S e takes P lace also in the female genitals; 

 mur; pti, patella; tb, the immediate surroundings become roughened and 



t, tarsus- ci^iaws.^' ' 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." 2 When fully 



matured the sexes, hitherto separated, come together, and the copulation 



takes place in a different manner by different varieties. 3 



The legs of the spider are eight, symmetrically disposed, 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 



Legs are numDcre( l fr m the face backward as first (1), second (2), 



third (3), and fourth (4) pairs. (Fig. 11.) The relative lengths 



are indicated by a formula composed of the above numerals arranged in 



the order of greatest lengths from highest to lowest, thus: 1 2 4 3 is the 



formula which expresses the prevailing order among Orb weavers and de- 



'. Aranr;r Svc<-i;i-, ]>.i^c 12. 

 , "l>ir I'rcllssisclic S|iililK-n." 



See Chapter on " Wooin.i: and Mating Habits," Vol. II. 



