10 



ARACHN1DA. 



first is somewhat large, and is directed towards the middle line ; 

 out of this the masticatory blade-like appendage of these limbs 

 is developed. These blades, as we have shown, are of importance 

 in comparing Scorpio with Limulus. It is a significant fact that 

 the embryo, according to Laurie, has these appendages on all the 

 four pairs of limbs, while in the adult they are found only on 

 the first two pairs (in the Pedipalpi on the second pair only 

 (Plirynus)). 



With the segmentation of the limbs, which takes place somewhat 

 late (in the stage depicted in Fig. 7 (J), the embryo approaches 



Fig. 7.— Three embrycs of Euscorpius italicus (after JIetschnikoff, from Balfour's Text-book), 

 ab, post-abdomen ; ch, chelicerae ; pd, pedipalps ; j' 1 -^ 4 , the four ambulatory limbs ; pe, the 

 pectines (combs) ; st, stigmata. In the middle line is the neural groove, and at its side the 

 rudiment of the ventral chain of ganglia. The cephalic pits are visible on the cephalic 

 lobes in A and B, and the median eye in C. The transverse markings on the abdomen are 

 the result of the internal segmentation caused by the primitive mesodermal segments. 



the adult form (Figs. 8 and 7 C). The limbs lengthen at the same 

 time, and the rest of the body undergoes the modifications described 

 above. The appendages of the first abdominal segment [second 

 according to Brauer] degenerate, while those of the second 

 segment [third of Brauer] increase in size and develop transverse 

 furrows, which indicate that we have here the rudiments of the 

 pectines (combs). Important modifications occur in the four 

 following pairs of limbs, invaginations, which lead to the develop- 

 ment of lungs, forming on their dorsal sides (Laurie). As these 



