l'i'()('('|)Ii;ilic L(i|)cs (if M|)cir:i ( 'iiicrcii. 117 



fouTul tliat, in its later condition, it consisted of a principal cerebral 

 mass which is connected with the sub-ocsophageal ganglia by a pair 

 of commissures consisting' of the two halves of the clu^liceral segment; 

 the sub-<Psophageal mass consisting of the remaining thoracic ganglia. 



Locy, in his pa]iei- <mi the dcnclopniciil of A(/aleria nwvia, fiiiled 

 (o add mu(di l<> the cxisliiii;' knowledges of I lie cei-ebra! lobes; although 

 he successfully foll(t\\<(l (he developiiieiil. of llic iinlei-ior median eyes 

 which, in their foi-iimt ion, are iiil iiiuitely associated with the develop- 

 ment of the anterior lobes of I lie brnin. 



Kishinouye's acccjuiit of llie (le\'elo|»iiieiil of llie brain of the spider, 

 while in some respects more satisfnctoi-y I ban that given by bis prede- 

 cessors, still leaves much to be said, lie slates that the rudiment of 

 the cxintral nervous system is laid down very shortly after the forma- 

 tion of the germ band, and that the ectodc^rm of tJui (cephalic plate is 

 broken up into ridges by the for-iiial Ion of successive transvfirsc thick- 

 enings which are coiit iniious with simibir thickenings that aj)pear 

 later on the inner margins (»f llie bileral bamls of llie end>ryo. '^Fhtise 

 thickenings, wliich appear in llie eclodenn of llie cepludic plate, indi- 

 cate the Ix'ginniMg of llie ganglia of tln' brain. Tliose which appear 

 on the lateral halves of llie v(!iitral plate form the rudiment of the 

 nerve cord. 



Balfour, Locy aiul K isliinouye rec<)giii/,e llie relations which the 

 crescentic invaginations, ^\■lliell iippear on the anterior margin of the 

 ceplialic ])latc, bear to the formal ion of Ibe anlei-ior vesicles of the 

 brain. They are able; to acc()unt for llu; formation of the lateral 

 vesicles from similar, though smaller, invaginations which appear 

 on the lateral mai-gins of the plalc K'ishinoiiye states that the 

 anterior vesicles form the principal mass of tlu; bi-ain, but he failed 

 to relatx' them, as Locy does, with the develof»ment of the antx'rior 

 median eyes. 



Patten (34, 35, and ;U'» ) called attention to the significance of the 

 appearance of pre-oral segments in the cephalic plate of Arthropods, 

 and ])ointed f)ut that such seginents wen; similar in charactfir to 

 those which were j)ost-oral in position and bore appendages. IFo was 

 able to show that the segments of the cxjphalic plate were divided by 

 distinct thickenings of the ectoderm into c(>rebral and optic ganglia, 



