XI 



PHYLUM ARTHROPOD A 



655 



One, two, or three receptacula seminis (rec. sem.) are present, and 

 either open into the vagina or independently on the surface. In 

 the male there are two elongated tubular testes with two narrow 

 and often greatly coiled efferent ducts, which unite in a short 



FIG. 564. Main branches 

 of the tracheal system 

 of a Spider. .<?. 

 stigma. (From Hertwig, 

 after Bertkau.) 



FIG. 565. One of the book-gills of Limulus, with 

 the appendage to which it is attached. (After 

 Lankester.) 



median vas deferens, the aperture of which is on the base of the 

 abdomen between the stigmata of the first pair. The pedipalpi 

 of the male (Fig. 555) are modified to act as intromittent organs : 

 the terminal segment is swollen, and contains a twisted tube (sph.) 

 into which the sperms from the reproductive aperture are received 

 in order to be transferred ^ ens 



in the act of copulation ^r\ 



to the reproductive aper- 

 ture of the female. The 

 eggs of spiders are laid 

 in nests or cocoons, and 

 are usually guarded by 

 the mother, sometimes 

 carried about by her. 



In their mode of life 

 the Arachnida present 

 almost as great a diver- 

 sity as the Insecta. 

 Some Acarida are para- 

 sites throughout life. 

 Most of the other groups 

 of Arachnida are pre- 

 daceous preying for the 

 most part on Insects or other Arachnids. To capture the Insects 

 which constitute their food, the majority of Spiders construct a web 

 formed of the threads secreted by the arachnidium. The primary 



nervf 



FIG. 566. Section of the lateral eye of Euscorpius 

 italicus. int. intermediate cells ; lens, cuticular 

 lens ; nerv. c. terminal nerve-cells ; nerv . f. nerve- 

 fibres of optic nerve ; rhabd. rhabdomes. (After 

 Lankester and Bourne.) 



