Coxal Glands o/' Scorpio. 59 



often erroneously called the " liver." The Malpighian tubules 

 have here, as it appears to me, become specialized for the 

 removal of fsecal matter from the tips of the diverticula*. 

 In this case the waste products appear to be entirely used up 

 in the formation of silk. 



We find, then, a distinct physiological connexion between 

 the purely excretory glands and the silk-glands ; when the 

 latter are well developed, the former tend to atrophy or to 

 become specialized for other functions, and, on the other 

 hand, when there are no glands for using up the waste products 

 the purely excretory glands are well developed. This 

 physiological relationship need not necessarily imply any 

 homology between the spinning- and poison-glands, on the 

 one hand, and the excretory glands (coxal glands and Mal- 

 pighian vessels) on the other. At the same time the common 

 derivation of all these glands from setiparous sacs would 

 render such connexion very natural. 



EXPLANATION OF PLATE 11. 



Fig. 1. A transverse seciion oi Euscoi-pio italicus, passing tlirough the tip 

 of the coxa of the fourth leg, c^. c^, coxa of third leg, the pos- 

 terior face of whicli is fused with the anterior face of c^, leaving, 

 however, an open channel, ch ; en, eudosclerite ; n, nerve to the 

 third leg (the accompanying blood-vessel gives off a branch, b, 

 to the coxal gland) ; sp, sternal plate. 



Fig. 2. A few sections further tack, showing the part of the duct {d) 

 leaving the chitinous channel {ch), and the blood-vessel {b) 

 running backwards. The coil of the coxal gland is also cut 

 through taugentially ; nuclei in various stages of vesicidation 

 ai'e found, the largest and most vesicular being detached. 



Fig. -i. A portion of the cuticle of Falavinceus Tho)-ellii, Focock, macerated 

 in caustic potash, showing the posterior face of tlie coxa of the 

 third leg seen from within, ma, chitinous attachments for 

 muscles ; ch, the channel between c^ and cl ; d, chitinous intima 

 close to the aperture of the duct ; sp, portion of the sternal 

 plate. 



Fig. 4. Anterior section through the end-saccule ^the so-called " medul- 

 lary substance ''). The clear portions are the blood-passages, 

 the dotted parts are the tubules of the end-saccule. Tlie opening 

 of the blood-vessel is marked by a curious agyrregation of cells (c) 

 (? Sturany's " Plutzelleu '') between which the blood flows. 



Fig. 5. Posterior section through tlie end-saccule, showing that the latter 

 is but an expansion of the coiled duct. Between the scattered 

 epithelium of the end-saccule and the highly specialized epithe- 

 lium of tlie coiled duct occurs a short baud of epithelium appa- 

 rently quite undifferentiated. 



Fig. 6. Diagram of the gland, showiug the .•special blood-vessel discharging 

 its contents among the tubules of the end-saccule. Lettering as 

 above. 



* "Notes on some of the Digestive Processes in Arachnids," Journ. R. 

 Micr. Soc. (in press). 



