Herrick, Cerebrum of the Opossum. 17 



nucleus alone stains in most instances and this not deeply. A reticu- 

 lum within the clear nucleus is brought out, but, as a rule, no distinct 

 nucleolus. Where the cell contour is visible it is as described above. 

 Such cells are associated with the deeply stained pyramids in such a 

 way as preclude the view that the difference could be due to varying 

 treatment. 



The distinction once relied on by us, i. e. the direction persued 

 by the apical process does not seem constant here. The deeper cells 

 have the apical process directed entad while the ectal series may have 

 the reverse position. The dorsal portion of the occipital region is oc- 

 cupied by these flask cells almost to the exclusion of all others. In 

 longitudinal section at the poserior part of the cortex the following ob- 

 servations were made. There are here few pyramidal cells and a rel- 

 atively large number of pale cells which contain large clear nucleoli 

 and chromatin (?) mesh-work. The cell body is frequently so incon- 

 spicuous as to make the nuclei appear like free corpuscles. In many 

 cases sufficient care will detect the cell outlines and in other spaces in 

 the neuroglia testify of their presence. The outline of the cell is rare- 

 ly as distinctly pyramidal as in the motor type through peripheral pro- 

 cesses in some cases at least pass dorsad. See plate C, Fig. 6, which 

 is a drawing of a portion of the occipital region (IV — 7. ) as seen with 

 the one-fifth inch objective. ///. is one of the pyramids and s. one 

 of the supposed sensory cells. The almost constant presence of Deit- 

 er's cells at the base of the pyramids will be noticed. This region 

 may be contrasted wit a typical motor area as drawn in Fig, i of the 

 same plate or Fig. 2. A mixed area some distance beneath the ectal 

 layer of cortex is drawn in Fig. 1 1, Plate A. In this case the sensory 

 cells are almost unstained except the nucleus. (4 — 14.) In even the 

 typical motor regions these pale cells are always present though in less 

 numbers and mostly crowded to lower levels. Toward the posterior 

 part of the hemispheres the cortex along the middle of the lateral 

 aspect differs quite obviously from any other portions. The band is 

 rather narrow and consists of small and slender cells which are in 

 many cases pure fusiform elements, others are flask-cells, or rather 

 inverted pyramids, but careful examination with one fifteenth inch 

 objective (1500 diameters) shows that the process directed proximally 

 does not form a single axis cylinder, as appears at first, but dissolves 

 into several small fibres. Among these cells are a i^v^ with the usual 

 pyramidal structure, but more slender than usual. Near the white 



