COURTSHIP AND MATING 93 



domen of a female of the stocky crab spiders is often so wide that 

 the male must crawl to a ventral position in order to apply his 

 short palpi. 



The actual copulation, accomplished by means of the secondary 

 genital structures, consists in the orientation and pressing of the 

 embolus into the atriobursal orifice of the female. Many of the 

 primitive spiders that use the Dysdera embrace apply both the palpi 

 simultaneously to the orifices just beneath the genital furrow. Since 

 both palpi are applied directly from beneath, it follows that the 

 right palpus enters the left orifice, and the left palpus the right 

 orifice, of the female. Other spiders of that series, for example the 

 tarantulas and their allies, apply each palpus alternately, but prob- 

 ably use the same side for insertion as indicated above. In all the 

 higher spiders this situation is reversed, with corresponding palpi 

 serving the corresponding female orifices. This most interesting fact 

 indicates that specialization in the epigynum and palpus has been 

 accompanied by profound changes in the insertion of the embolus. 



The actual union of the secondary genital structures may be of 

 very brief duration, only a few seconds, or it may be prolonged 

 for several hours. When the organs are highly complicated, the 

 insertion is apparently aided by a preliminary lubrication of the 

 palpus accomplished by drawing it through the chelicerae and is 

 finally consummated only after the manipulation of several different 

 elements. The palpus may be scraped across the epigynum until a 

 spur on the tibia, on the tarsus, or on the bulb itself becomes fixed 

 in a particular groove. Once firmly anchored in this starting point, 

 the palpus swings to assume a position that, with the aid of ridges, 

 grooves, and other processes on the epigynum corresponding to its 

 own outline, makes it possible to guide the embolus to exactly the 

 right point for entering the orifice. At this stage, the bulb of the 

 palpus is still largely in its resting position, lying folded in the cup 

 of the tarsus, and the preliminary contacts serve to hold it firmly 

 in place. Most spiders have at the base of the bulb various thin 

 pouches, or hematodochae, that swell up with the influx of blood 

 until they attain enormous size. This distention causes the entire 

 bulb to turn on its axis, which action forces the embolus into the 

 appropriate opening. The whole embolus (usually a thin spine or 

 heavy spur but often a coil that may consist of several turns) is 

 screwed into the epigynum, following the corresponding tubes in 

 this organ until it reaches the receptaculum seminis. Semen is then 

 pumped into this receptacle by means of a strong blood pressure in 



