EPEIRA, 237 



long coiled nialpighian tubules opening into the cloaca. In 

 addition to possessing two kinds of excretory 

 xcre ory. ^j-g^^^g^ ^^ spider also has two kinds of respira- 

 tory organs. The two pulmonary sacs are situated in the 

 antero-ventral part of the abdomen and consist 

 espra^ory. ^^ large chambers containing a number of flat 

 horizontal lamdlce with thin walls. Stigmata put their 

 cavities in communication with the exterior. There are in 

 addition four tracheae opening, as stated, by a ventral 

 aperture in front of the spinnerets. They do not differ 

 essentially from the tracheae of the insects. Hence the 

 spider has two sets of breathing organs, pulmonary sacs 

 and tracheae. 



The ovaries are paired tubes uniting to form oviducts 

 which open into a median uterus. The uterus opens into 



« ^4.4 the genital pouch, into which also open 

 Reproductive. ^ & . / ' , „., , ^ . 



two seminal receptacles, Ihe pouch is 



provided with a kind of gonapophysis, called the epigy- 



nium. The testes are simple tubes with vasa defer entia 



uniting into a sperm-sac with a median aperture just behind 



the stigmata. 



The eggs are laid in holes and corners during the autumn, 



and are often enveloped in silky cocoons. They have a 



-. , ^ large amount of volk, and the development 



Development. . ° , . n-u u *. u • *^u • 



is embryonic. Ihey hatch in the spring, 



the young spider differing but Httle from its parent. The 



spiders form the order Araneina of the class Arachnida. 



(For General Characters of Sub-Phylum Arthropoda, 



see page 240). 



PHYLUM ANNULATA. 



The Annulata form one of the three great phyla of the 

 Metazoa. They are typically elongated piano-symmetric 

 animals. They always have three primary layers, the meso- 

 derm filling more or less of the space between the ectoderm 

 and endoderm. The whole body is segmented or made up 

 of a number of segments or metameres, in which many 

 organs are repeated. In the lower types there can be dis- 

 tinguished a pre-oral part, in front of the mouth, called the 

 prostomium, and a segment immediately behind the mouth 



