96 AMERICAN SPIDERS 



are known among the mites, where the chelicerae or legs are used 

 to transfer the semen. 



The final step in araneid copulation is the modification of the 

 appendage into an organ where the sperm can be stored some time 

 before pairing. Having the semen secure in a reservoir at the end 

 of the palpus does away with the need of ejaculating it during or 

 immediately preceding the mating, and lessens the risk of losing the 

 female during such a preliminary routine. The intermediate stages 

 of the araneid mode of copulation have been dropped out com- 

 pletely, and do not even persist in some form in the memory of 

 the race. What we see is the culmination of the whole process, 

 something unbelievably complicated, the proper performance of 

 which is part of the instinctive makeup of the male spider. 



The palpus of the male only gradually developed into the com- 

 plicated organ we now observe. At first it resembled that of the 

 female, and was armed at the end with a single tarsal claw that 

 picked up the spermatophore and pressed it into the female vulva. 

 Gradually the claw became transformed into a cup-shaped recepta- 

 cle, from which the liquid was less easily lost, and finally the cup 

 was closed at the end until only a small opening remained through 

 which to take in and drain out the semen. This receptacle is the 

 all-important element of the palpus, and in its simplest form is made 

 of three more or less well-defined parts: a basal expanded portion 

 termed the fundus, a coiled intermediate tube called the reservoir, 

 and the delicate terminal ejaculatory duct. We see this elementary 

 receptable in the palpi of many spiders where it has remained very 

 simple, and can still discern it as the prime element of those in which 

 the structure has become greatly elaborated. 



At first, the receptaculum seminis was appended to the tarsus as 

 a simple extension, but in this position it was quite liable to be 

 broken or injured in some way. Specialization has proceeded to 

 protect it and its delicate terminal duct, and to make it more effec- 

 tive as an intromittent organ. Around it has been developed a pro- 

 tective cover called the bulb. The tarsus itself has been excavated 

 to form a receptacle in which the whole organ can lie when at rest. 

 Muscles and blood pouches have been evolved to make possible the 

 ejection of the semen. On the bulb itself have arisen processes that 

 are used to orient the parts of the palpus in relation to those of the 

 epigynum, and apophyses on the tibial and other palpal segments 

 to act in a similar manner. 



As is true for the male, the gonads of the female are hidden deep 



