666 Journal of Comparative Neurology and Psychology. 



and the myxinoids respectively. The chief topics of considera- 

 tion in each book are, the morphology of the vertebral canal and 

 cranium, the meninges and the blood vessels and lymphatics, 

 the sheaths of the nerves, and the central nervous system, par- 

 ticularly its hypophysis and membranous parts. In short, the 

 non-nervous parts of the brain receive especial attention, with 

 particular reference to the factors of nutrition, metaboHsm and 

 mechanical support. All of these subjects are treated from the 

 embryological point of view and the developmental stages are 

 fully figured. The form relations of the brain are studied em- 

 bryologically and their comparative morphology considered, but 

 the volume contains no other descriptions of internal architec- 

 ture. Neither the fiber tracts nor the cellular masses are con- 

 sidered. 



These researches and many others along the same lines have 

 drawn attention to some very important types of relation between 

 the nervous and the other organs of the body, chiefly mechanical 

 and nutritive. But after all, the principal avenues of relation of 

 the nervous system are the nerves themselves. The sense organs 

 and the organs of response are the immediate instruments of almost 

 all animal activities and the central nervous system reflects every 

 change in peripheral relations. This reflection, however, is not 

 a transient and passive return of the nervous impulse from the 

 receptive to the eff'ective periphery as a light beam rebounds from 

 a mirror; it involves an active process of coordination during the 

 process, and — what is far more important from our present stand- 

 point — a permanent structural change in the coordinating mech- 

 anism itself. 



The cerebral architecture of every animal species has unques- 

 tionably been shaped by its peripheral nervous organs. As 

 animals gradually change their mode of life and different sets of 

 environmental forces impinge on the sensorium, the receptive and 

 efi^ective peripheral organs gradually undergo parallel changes 

 adapted to render the animal more fit to meet the changed environ- 

 mental conditions. And the central correlation apparatus of these 

 peripheral organs must change its form at the same time or the 

 whole process of the selection of adaptive variations would be 

 abortive. The structure of the central nervous system is in fact 

 very sensitive to changes in environment or mode of life. The 

 eyes of cave animals atrophy; so also do the visual centers of the 



