Herrick, Cerebrum of the Opossum. 19 



the cells regarded as kinesodic generally have their apical processes 

 directed peripherad (the converse being the case with the assthesodic,) 

 it must be said that too much confidence should not be placed in this 

 distinction. We now believe that the direction of the apical process 

 is to be interpreted as a function of the direction from which the cell 

 has migrated. We have shown in a series of papers that there is 

 morphological and embryological evidence that the cortical cells are 

 not formed in situ but have migrated fj-om proliferating areas primarily 

 found in the axial lobe. This suggestion has recently been greatly 

 emphasized by the discovery that the a.xial lobe of fishes contains 

 well marked areas of the two kinds of cells sustaining the proper re- 

 lations to the tracts to enable us to identify them as motor and sensory 

 respectively. It is believed that the motor areas of the cortex are 

 supplied by cells which migrate from before backward and first lodge 

 in the cortex, whence many subsequently migrate to deeper zones. 

 Such migrating cells retain their connection with the peripheral source 

 by means of the long apical processes. Sensory cells, having in many 

 cases a different path of migration, naturally occupy different positions. 

 In view of the recent results of Golge's method of staining, it would 

 be premature to decide how i^x these processes are simply nutritive 

 and how far actually nervous. It is significant, however, that the 

 processes of nutrition apparently go on at the base of the cell as indi- 

 cated by the nutritive nuclei there collected. 



PLATE A. 



A series of transverse sections through the cerebrum of tlie opossum. 



Fig. I. Section through the olfactory lobes. 



Fig, 2. Section at the junction of the crus and post-rhinal lobe near the 

 union of the rhinalic and splenial fissures. 



Fig. 3. Section through the fore part of the cerebrum. 



Fi^. 4. Section through the anterior commissure and fornix body. 



Fig. 5. Section at the caudal part of the anterior commissure, showing 

 tlie encroachment of the radix lateralis mesad and the dorsal sac. 



Ftg. 6. Section through the praethalamus and chiasm 



Fig. 7. Section through the mesencephalon at the posterior commissure 

 and hippocampus. 



Fig. 8. -Section through the occipital portion of the cortex and nates. 



Fig, 9. Section through the cerebellum and pons. 



