Susanna Phelps Gage • 427 



to the above observations, while the comparative studies on lower forms 

 lend their quota to the results 



These conclusions were stated by me in the above-mentioned 

 abstracts."" ^° Johnston/^ the latest reviewer of the serial order of seg- 

 ments of the head, does not agree with my view. His work is largely 

 based on immammalian material which in my experience, as above stated, 

 does not show the facts clearly being obscured by either thickened walls 

 or secondary formation of a neural cavity. The crucial point on which 

 he rests the conclusion that the olfactory is in front of the eye is depend- 

 ent upon those observations which tend to show that; (1) The segmental 

 mesoderm extends past the eye to the olfactory region; (2) The hypo- 

 physial thickening of the skin is continuous with the nasal epithelium 

 in petromyzon. With regard to the first point attention is called to a 

 recent paper by Froriep ^ in which he shows that the original mesoderm 

 of the head does not primarily pass cephalad of the hypophysis upon the 

 mesal line. As to the second point, Lubosch '* shows that the thickened 

 epithelium of hypophysis and olfactory plates is not continuous but is 

 separated by an interval of thin epithelium. Moreover, it is shown inci- 

 dentally in his figures, that it is in close connection with this thin mesal 

 plate that the incipient cavity of the eyes originates, that is between 

 hypophysis and olfactory. 



In order to make his contention good, Johnston is driven to the con- 

 clusion that the eye is a dorsal organ lying between the olfactory region 

 and the diencephal and in the course of development, is dragged ventrad 

 to its final position, the cerebrum and the eye being portions of the same 

 neuromere. The observation that the eye vesicle is originally at the edge 

 of the neural plate between hypophysis and olfactory region seems to 

 make this device unnecessary. 



The question of the cephalic end of the brain is not, to what point the 

 neural plate is cleft after the formation, and final growth of the meso- 

 derm into the head, but to what point it was cleft at the outset. As above 

 stated, in mammals and torpedo, the cleft originally extends to the hypo- 

 physis. The eye lies next to the hypophysis and distinctly intervenes 

 between hypophysis and olfactory region. 



More recent investigations on invertebrate brains/' seem to have 

 established the fact that the lobe of the brain connected with the com- 



^ Johnston, J. B., Jour. Comp. Neurol. & Psychology, XV, 1905. 

 =' Froriep, A., Anat. Gesell., Verhandl. 16, 1902. 

 ^'Lubosch, W., Morph. Jahrb., XXIX, 1902. 



-Comstock, J. H. and Chujiro Kochi, Am. Nat., XXXVI, 1902. They 

 summarize the work, including Patten's, from 1775-1900. 



