THE NERVOUS SYSTEM AND THE EYES. 



13 



In the rudiment of the brain, and especially in those parts of the 

 cephalic pits "which take part in its formation, there occur the same 

 small depressions which "were mentioned above in connection with 

 the formation of the chain of ganglia, and "were regarded as the 

 formative area for ganglionic cells (Kowalevsky and Schulgin, 

 Laurie). When the brain separates from the cephalic pits, it seems 

 at the same time to lose its connection with the ectoderm. 



With the brain are united the ganglia of the cheliceral segment 

 (Kowalevsky and Schulgin), a corresponding connection being 

 found in the adult. The two pairs of cheliceral nerves thus have 

 their origin in the brain, which is divided into an anterior portion, 

 giving origin to the optic nerves, a small middle unpaired portion 

 giving origin to the nerves of the rostrum, and a posterior paired 



B. 



,-e 



■ 



/ 



F IG . g.—Euscorpius italicus (after Laurie). A, transverse section through the anterior part 

 of the embryo ; B, anterior part of an embryo spread out flat, and seen from the ventral 

 side ; C, sagittal section through the head, a, rudiment of the median eyes (lenses) ; ch, 

 chelicerae ; e, cephalic pits; g, brain; p lt p~, first and second ambulatory limbs; ped, 

 pedipalps ; vd, stomodaeum. 



portion giving origin to the cheliceral and sympathetic nerves. The 

 thoracic ganglia and those of the first two [? three] abdominal 

 segments unite to form the large sub-oesophageal ganglionic mass in 

 the thorax which approximates to the brain. The number of ab- 

 dominal ganglia becomes reduced, by this fusion of some of the 

 anterior pairs, to seven (four probably belonging to the pre-abdomen, 

 and three to the post-abdomen). Some of the above facts were 

 made known through the researches of H. Rathke (Xo. 28) as 

 early as 1837. 



The formation of the median eyes is connected with that of the 

 supra-oesophageal ganglion, inasmuch as both can be traced back, in 

 part at least, to the cephalic pits. It has already been stated that 

 these pits are said to take part in the formation of the brain. It is 



