310 ARACHNIDA PEDIPALPI CHAP. 



genital opening and two pulmonary stigmata, while the other 

 stigmata are behind the second ventral plate, which corresponds 

 to the third abdominal segment. On the last abdominal 

 segment there are often two or four light-coloured spots called 

 " ommatoids," and considered by some authors to be organs of 

 sight. Laurie, however (vide infra), thinks it more probable 

 that they are olfactory in function. 



The Schizonotidae (see p. 312) have a two-jointed carapace, and 

 do not possess more than two eyes. There is a short unjointed 

 tail-piece. 



In the Tarantulidae (Phrynidae) the whole body is much 

 flattened and extended laterally, the undivided carapace being 

 reniform, and broader than long. The long non-chelate pedipalps 

 have their basal joints free and movable, and there are several 

 sternal plates. There are nine abdominal tergal plates, the last 

 three diminishing rapidly in size, and the last plate covering 

 a button-like terminal portion of the abdomen. The first 

 abdominal ventral plate is largely developed, as in the Thely- 

 phonidae, and the genital orifice and pulmonary stigmata are 

 in the same situation as in that group. The Tarantulidae have 

 glutinous glands in the first abdominal segment which are capable 

 of spinning a few irregular threads. 



In the whole group paired circular depressions are conspicuous 

 dorsally on all the abdominal segments. These indicate the 

 points of attachment of the dorso- ventral muscles. 



Internal Structure. The anatomy of the Pedipalpi has been 

 very inadequately studied. Disconnected notes 011 various points 

 of structure have been published by various morphologists, but 

 no complete investigation has yet been made of the internal 

 organs. This is largely due to the difficulty of obtaining 

 material, and the bad state of preservation of the internal parts 

 of such specimens as have been available for dissection. 



The following points have been made out in the anatomy of 

 Thelyphonus. 1 



The alimentary canal commences after the mouth with a 

 pharynx which, though not dilated, is furnished with sucking 

 muscles. It then narrows into an oesophagus which passes 

 through the nerve-mass, and afterwards dilates to form the mid- 

 gut, which immediately gives off two large lateral diverticula 



1 See M. Laurie in J. Linn. Soc. Zool. xxv., 1894, p. 20. 



