354 



PHYLUM ARTHROPODA. 



The spinnerets (4-6) lie posteriorly a little in front of 

 the anus. They are movable organs, perforated by numer- 

 ous (often many hundred) fine tubes or " spinning spools." 

 The tubes are connected with numerous compressible 

 glands secreting liquid silk. There are various kinds of 

 glands, and both the amount and the nature of the secre- 



o 



tion are under the spinner's control. The spinnerets arise 

 from modifications of abdominal appendages, and the glands 

 are ectodermic invaginations. 



Many spiders have at the base of their spinnerets a 



transverse surface or cribrel- 

 lum perforated by spinning 

 tubes, and from this they 

 comb out a peculiar curled 

 silk with the help of a row 

 of stiff bristles or calamis- 

 trum on each posterior leg. 



The males are usually 

 smaller and often more 

 brightly coloured than their 



FIG. I73 .-Section of Lung-book. mates " . Fr0m the P aired 



-After Macieod. " testes, in the anterior part of 



, the abdomen, two vasa defer- 



a., Dorsal ; z>., ventral ; /., lamellae ; j$., 



posterior ; a., anterior ; d.c., dorsal Clltia paSS tO a Common 

 chamber ; jr., posterior wall ; st., 

 ch., one of the interlamellar 



tn Kpcirlp fhp nnpnincrs nf 

 '65106 HlC Openings 01 



chambers. the lung-books. From the 



paired ovary two oviducts 



likewise arise and open into a uterus, whose external aper- 

 ture is surrounded in the mature female by a complex genital 

 armature or epigynium. Here also in most females are the 

 openings of two receptacula seminis, in which the sperms 

 received from a male are stored, and from which they pass 

 by a pair of internal ducts to the oviducts, there to fertilise 

 the ova. The sperms of the male, after emission, may be 

 stored up in the last joint of the palps. The ova are usually 

 surrounded by silken cocoons, which are carried about by 

 the mother or carefully hidden in nooks or nests. There 

 is no metamorphosis, but spiders at birth are often very 

 different in details from their later stages. 



Spinning 1 . Compression of the spinning-glands causes a flow of 

 liquid silk through the fine spools of the spinnerets. The extremely 



