— 20 - 



According to Kleinenberg (25) part of the nervous 

 system of Lopadorhynchus is also formed out of primitive 

 sense-organs, which afterwards become converted entirely 

 into ganglion-masses. 



We are thus led to suppose that the central nervous 

 system of Arthropods to some extent corresponds in origin 

 and structure to that of Vertebrates; namely, as regards 

 the origin of the three layers (" Saulenschicht," "Mittel- 

 zone," and "Randschleier'' "surface pit", germ-group, 

 and commissural substance), and as regards the conversion 

 of sense-organs into ganglia. To some extent it corres- 

 ponds to that of Molluscs, namely, as regards the origin 

 of ganglia out of sense-organs, and perhaps in possession 

 of an accessory brain. Lastly to that of Worms, namely, 

 as regards the origin of ganglia out of sense-organs. 



The Median Eyes. — As yet only the median eyes 

 have begun to make their appearance. Being unpig- 

 mented they are not visible on surface views. T.ie lateral 

 eyes are first met with in more mature stages. Just above 

 the chelicerae, on the front of the cephalothorax, we meet 

 on each side with a lappet-like excrescence, the bases of 

 which have already begun to unite with each other where 

 they meet in the median plane; thus they form a kind of 

 mask in front of the embryo, covering its mouth. The 

 space beneath this mask remains hollow till much later. 



These folds are the Anlagen of the median eyes, 

 they consist of two simple thickenings of the ectoderm, 

 which have probably been inverted in the way described 

 by Brauer for Scorpions. 



The front wall of the eyes still only consists of a 

 single row of cells; in the posterior wall the cells have 

 begun to multiply. The space between the anterior and 

 posterior walls of the eyes contains no nuclei, being only 

 filled with cell-walls and plasm. 



The eyes measure in length *1 mm., they are *04 mm. 

 thick. 



Besides the eyes there is only one other set of 

 sense-organs to be found. These are the segmental sense- 

 organs first described by Patten (34) as occurring at the 



