INTRODUCTION xi 



lungs, and between them the opening of the reproductive 

 organs (fig. i). The latter is covered in females by an appa- 

 ratus, sometimes large and complicated, called the epigynum. 

 Its presence shows that the female is full grown. Young 

 spiders do not have it. Male spiders have the ends of the palpi 

 enlarged, and under the terminal joint what is known as the 

 palpal organ, sometimes very complicated in shape. The pres- 

 ence of- these organs shows that the male is full grown. 

 Young males that have nearly reached maturity have the ends 

 of the palpi simply enlarged. Male spiders almost always have 

 the body smaller and the legs longer than females of the same 

 species. 



The colors of spiders are partly in the skin itself and partly 

 in the hairs and scales that cover it. Almost all spiders are 

 covered with hair of some kind, but in some species it is so 

 fine and short that it has little effect on the color. In others 

 the skin is entirely covered with hairs of various lengths and 

 sometimes with scales somewhat like those of butterflies, flat- 

 tened and feathered or toothed on the edges. The colors of 

 spiders are very varied, and in many species, especially of the 

 jumping spiders, as brilliant as those of butterflies. The most 

 common colors are grays and browns, resembling the ground 

 or plants and stones among which the spiders live. Sometimes 

 the color is uniform all over the body, except that it is a little 

 darker toward the head and the ends of the feet. The most 

 common marking is a spot on the front of the abdomen over 

 the spider's heart, sometimes merely a translucent part of the 

 skin and sometimes a definite color spot darker in the middle 

 and outlined with a lighter shade or white. The hinder half 

 of the abdomen is often marked with several pairs of spots, 

 becoming smaller toward the end, and these spots may be 

 united into a pair of stripes or a more complicated pattern. 

 (See figures.) The legs are often marked with rings of color, 



