ARTHROPODA. 303 



basilar somite is ^composed of four embryonic somites to which the appendages 

 Figs. 8-10 belong, one of the somites being limbless. He believes that the 

 basilar somite corresponds to the poison claws, Fig. 9, alone, and that there is 

 no somite without a limb. At any rate there is none in Geophilus, according to 

 Metschnikoff. 



Cf. Meinert, Caput Scolopendrae, Copenhagen, 1883; cf. Journal R. Micr. 

 Soc. 1884, p. 374, and Amer. Naturalist, xviii. 1884. 



Poison glands. MacLeod, Bull. Ac. Roy. Belg. (2) xlv. 1878. 



FIG. ii. Geometrical Spider, Epeira fasciata, viewed from below. Regne Animale, Les 

 Arachnides, by Duges and Milne Edwards, PI. XI. Fig. \b. 



a. The chelicerae or falces. These limbs are post-oral in the embryo 



but prae-oral in the adult. They consist of a large basal and a 

 slender claw-like terminal joint, at the top of which opens the duct 

 of the poison gland, seen at /, in Fig. 12. This joint moves 

 horizontally in all Spiders with the exception of the Tetra-pneu- 

 mones (Mygale and the Trap-door Spiders). 



b. Pedipalpi, consisting of a limb-like terminal portion and an enlarged 

 basal or masticatory joint. Between the two basal joints is the 



lower lip or labium of authors. It has nothing to do with the parts 

 so termed either in "Insecta or Scorpio, but represents the prosternite 

 (cf. Ray Lankester, Q. J. M. xxi. 1881. p. 531, and Fig. 9, B.}. The 

 specimen from which this figure was taken was that of a female. 

 In the male the terminal joint of the limb-like portion or ' palp ' 

 of this appendage is modified to receive the sperm and act as a 

 copulatory organ. 



c. Mesosternite, surrounded by 



d. The basal joints of the four ambulatory limbs. 



The part of the body bearing the above-described limbs constitutes' 

 the cephalo-thorax. It is followed by the soft unsegmented abdomen 

 which, in the embryo Spider, consists of nine somites and a terminal 

 azygos piece. 



e. The stigmata leading to the two pulmonary sacs. 



f. Those leading to the tracheae. Between them is the epigynal organ 



covering the sexual aperture. 



g. The four spinning mammillae with the anal valve as a fifth lobe 



behind. Most Spiders, with the exception of the Tetra-pneumones^ 

 have six mammillae. The Tetra-pneumones, as a rule, possess 

 only four. 



Auditory and olfactory organs. Dahl, A. M. A. xxiv. 1885 ; cf. A. N. H. (5) 

 xiv. 1884. On an organ of sense. Bertkau, A. M. A. xxiv. 1885, and Id. and 

 Schimkewitsch, Z. A. viii. 1885. 



Respiratory organs, MacLeod, Archives de Biologic, v. 1885. 



