1906- 1907.] Observations on a Mygale Spider. 405 



deal of web — but, from our point of view, the most of it to 

 little purpose. The box it is kept in has two sides of glass, 

 the others being of wood. At one end it has a small nest or 

 den, where it spends a good deal of its time. Often, but not 

 always, after it has entered this den it runs a number of 

 silken threads across the entrance to keep out intruders. A 

 few months ago it spent many days in making a thick and 

 strong wall from the entrance of its den to the side of the 

 box. It has also covered the floor with a thick carpet of silk. 



The body of the spider is divided into two parts. The 

 head and chest are united, forming one mass, called the 

 cephalo - thorax. The hind part, called the abdomen, is 

 united to the cephalo - thorax by a short pedicel. The 

 cephalo - thorax is covered on the upper side with a hard 

 horny plate, which is called a shield. The under plate, to 

 which the legs are jointed, is called the sternum, or breast- 

 plate. Beginning with the head, the Mygalidse differ from 

 other spiders by having their falces or poison -fangs with 

 their points directed downwards, and moving vertically parallel 

 with each other. The poison-fangs of other spiders move in 

 a horizontal direction, with their points facing each other. 

 The fangs are hard and sharp, and have an opening near the 

 point, from which the poisonous fluid is ejected. 



On each side of the poison-fangs are the five-jointed palpi. 

 In the female they are long, leg-like, and terminate in a 

 single claw. The ocelli or simple eyes, eight in number, are 

 placed together on an eminence of the shield. Immediately 

 behind the poison -fangs the four largest eyes form a row. 

 At the back of each end eye of the row two smaller eyes 

 form with it a triangle. Spiders have eight legs. Each leg, 

 except in one small genus, is composed of seven joints. The 

 first is called the haunch, the second and third the thigh, the 

 shank and the foot each formed of two joints. In this spider 

 the leg terminates in a pair of claws, which are retractile, 

 like those of a cat. The last joint of the palpi and the two 

 last joints of the foot are densely clothed on the under side 

 with compound hairs, which enable the spider to climb up 

 glass and other smooth and polished surfaces. 



In the Mygalidse respiration is effected by four pulmonary 

 sacs, composed of a number of thin flat bags, called lung- 

 books, which open to the air by stigmata, situated on the 



