MOEPHOLOGY OF BEAIN AND SENSE OEGANS OF LIMULUS. 45 



authors as I would like. But in what follows I shall try to 

 show that their basis of classification of the brain-lobes is 

 founded on vital misconceptions. They fail to recognise 

 the difference between the organs derived from the cephalic 

 lobes and those derived from the ventral cord^ as well as the 

 segmental nature of the primitive optic ganglia in such forms 

 as Acilius and Scorpions, and their relation to the compound 

 eye. Moreover, when Viallanes subsequently attempted to 

 confirm his views by embryological study, he not only selected 

 in Mantis a poor type, but mistook the well-known trachea- 

 like invaginations for the ganglionic ones described by me, 

 and consequently he is quite right in asserting that they do 

 not give rise to any part of the optic ganglion. 



Those who have heretofore touched on the development of 

 the brain of Insects have failed to appreciate the far-reaching 

 morphological importance of the ganglionic invaginations. 

 Korschelt and Heider, in their text-book of embryology, did 

 not understand their relations in Insects, Scorpions, and 

 Limulus. As I consider these invaginations the key to the 

 morphology of the Arthropod and Vertebrate fore-brain, I 

 shall try to explain in more detail my interpretation of their 

 significance. 



In studying the development of the convex eyes great con- 

 fusion and difficulty was at first occasioned by the failure to 

 recognise that two distinct invaginations are sometimes pre- 

 sent, one for the optic ganglion, the other, less commonly 

 present, for the eye. Reichenbach and Kingsley made this 

 mistake; both supposed that the purely ganglionic invagina- 

 tion described by them gave rise either to the whole (Kingsley) 

 or a part (Reichenbach) of the ommateum. 



I was the first to show in Vespa that the two invaginations 

 are absolutely distinct, one giving rise to the three lobes of the 

 optic ganglion, the other to the compound eye. The latter 

 invagination, although very deep, probably does not close up, 

 and its outer or middle wall produce the corneagen, as I at 

 first supposed. Strangely enough, the invagination soon 

 straightens out, and the corneagen, as I found out subse- 



