Anatomy of some Scorpio7is. 191 



between two of the sternites, to extract the lung-book without 

 injury to the external appearance of the specimen. Treat- 

 ment for fifteen minutes with hot dilute caustic soda makes 

 tlie structure more distinct by removing the organic matter. 

 The anatomy of these structures is sufficiently well known, 

 and, as it seems to be constant throughout the group, need 

 not concern us here. The shape of the lamellfB varies too 

 much in the different parts of the lung-book to be of any 

 service, Lankester * used the surface-markings of the 

 lamellae in his classification, and distinguishes two types. 

 In one of these the whole of the upper surface of each 

 lamella is covered with small pillar-like structures, which 

 serve to maintain a space for the air between each pair 

 of lamellae. Berteauxf has shown that these rods or pillars 

 are in Scorpio indicus of two kinds. Those round the 

 margin of attachment are smaller than the others, and their 

 upper ends fuse to the lower surface of the lamella above. 

 The larger pillars which occupy the centre and free border of 

 the lamella do not fuse to the superjacent lamella, but fre- 

 quently divide at the top, and may form arcades by uniting 

 with adjoining pillars. These two regions of the lamella are 

 usually quite distinct from each other and easily made out. 



In Euscorpius jlavicaudis according to Berteaux the rods 

 nowhere unite with the adjoining lamella. The two areas on 

 the surface of the lamella are nevertheless quite distinct, at 

 all events, in Euscorpius italicus. 



In the second type of lamella the area occupied in the first 

 type by the larger pillars is covered by a network of chitinous 

 ridges, the meshes of which are subdivided by smaller ridges. 

 Pillars are entirely wanting over this region, but towards the 

 sides they begin to appear among the ridges, and finally 

 replace the ridges entirely. 



Berteaux has described a farther difference in various 

 forms in the structure of the free edge of the lamella. In 

 lamellae of the first type the edge may be furnished with 

 sharp spines (fig. 9), a condition which he describes in 

 Scorpio, or the spines may divide at their free ends, and, 

 uniting with each other, form a regular arcade (fig. 10), an 

 arrangement which occurs in Euscorpius. 



In the second type the network of ridges is present on 

 both surfaces of the lamella, the larger ridges being con- 

 tinuous over the edge, and the edges are devoid of spines 

 (fig. 11). 



* Loc. cit. p. 378. 



t Berteaux, ' Le Pouraon d. Arachnides,' " La Cellule," vol. t. 



