2 7 o AMERICAN SPIDERS 



Sexual dimorphism. A difference in form, color, size, etc., between 



sexes of the same species. 

 Spermathecae. The vessels or receptacles in the epigyna of female 



spiders that store the spermatozoa of the males. 

 Sperm web. A web of few or many threads on which male spiders 



deposit the semen preparatory to taking it into the palpus. 

 Sperm induction. The process of transferring the spermatozoa from 



the genital orifice beneath the base of the abdomen into the 



receptacle in the male palpus. 

 Spermatozoa. The mature sperm cells. 

 Spiderling. A tiny, immature spider, usually the form just emerged 



from the egg sac. 

 Spinnerets. The fingerlike abdominal appendages of spiders through 



which the silk is spun. 

 Spiracle. A breathing pore or orifice leading to tracheae or book 



lungs. 

 Stadium. The interval between the molts of arthropods; instar; a 



period in the development of an arthropod. 

 Sternum. A sclerotized plate between the coxae marking the floor 



of the cephalothorax. 

 Tarsus. The foot; the most distal segment of the legs, which bears 



the claws at its tip. 



Tergites. Dorsal sclerites on the body; the hard plates on the ab- 

 domen of the atypical tarantulas that indicate the segmentation. 

 Thorax. The second region of the body of insects that bears the 



legs; in spiders, fused with the head to form the cephalothorax. 

 Tibia. The fifth division of the spider leg, between the patella and 



metatarsus. 

 Tracheae. The air tubes in insects; in spiders, tubular respiratory 



organs of different origin; by many thought to be modified book 



lungs. 

 Zygote. The fertilized egg. 



