RKSI’IRATOHY ()R(iANS IN ARANKA']. 
103 
EXPLANATION OF PLATES 1—7, 
Illustrating Mr. W. F. Purcell’s paper on '•'Development and 
Origin of the Respiratory Organs in Araneae.” 
Stages in the Development. 
Stage 1 {St. 1), just befoi-e the appearance of the pulmonary furrows : 
figs. 4, 7, and 7a (all from same emhi-yo). 
Stage 2 {St. 2), with two pulmonary furrows: figs. 1, 5, 5a, 8, and 
8a-8h (5, 5a, 8, 8a-8h all from one embryo) ; figs. 9, 10, 14. 
Stage 3 {St. 3), with three pulmonary fun-ows ; figs. 2, 11. 
Stage 4 {St. 4), with 4-5 pulmonary furrows : figs. 12, 15. 
Stage 5 {St. 5), with 5-G pulmonary furrows : figs. 3, 6, Ga, and 27 
(G, Ga, and 27 from one embryo) ; figs. 13, 13 a, and 13 b (all from one 
embryo) ; figs. IG, 1 Ga-1Ge, 35, and 35 a (all from one embryo). 
Stage G {St. G), after end of reversion and shortly before hatching : 
figs. 17 and 43 (from same embryo) ; figs. 18, 28, 41. 
Stage 7 {St. 7), after hatching : fig. 34. 
Stage 8 {St. 8), after first post-embryonic moult : figs. 29 and 29a 
(from same embryo) ; fig. 30. 
Abbreviations for all the Plates. 
The yolk is coloured yellow in the figures representing sections, all 
of which have been drawn with the aid of a drawing apparatus. The 
letters {St. 1). {St. 2), etc., alongside the numbers of the figures denote 
the stage of the embryo from which the section has been made. 
a. ob. m. 8 and 10. Anterior oblique muscles of somites 8 and 10. 
«. spin. Inner openings of anterior pair of spinners, ah. app. 1-4. Ab- 
dominal appendages 1-4. ant. Anterior side. ap. Apical pouch of 
honi of pulmonary sac in developed lung-book. app. G. Sixth prosomatic 
apiDcndage. ar. 7-11. Areas in contact with the ends of the segments 
of the ventral longitudinal muscles of somites 7-11 at the time of the 
formation of the entochondrites. h.f. Basal fold of tracheal trunk. 
bd. c. Blood-coiqmscles. br. Branches of tracheal trunk, c. Cones of 
a cJiitinous saccule, can. Canal of communication, cent. Centre of 
section, cl. 1, cl. 2. Clefts on the distal side of first and second pul- 
monary saccules. coel. G-14. Ccelomic sacs of 6th-14th post-oral 
somites, cu. Cuticula. cu.', cu." Cuticula formed at first and second 
post-emljryonic moults, d. 1. m. 8-15. Segments of the dorsal longi- 
tudinal muscles in somites 8-15. d. v. 1. m. Longitudinal muscle along- 
side of the proctoda;um uniting the last segment of the dorsal with that 
