DEPARTMENT OF EMBRYOLOGY. 113 



In the work of Dr. Weed the individual interpretation of the many 

 nuclear masses has, as far as possible, been eliminated from his recon- 

 struction. Most of the collections of nerve-cells have been delimited 

 under low magnification, with later substantiation of their limits under 

 higher powers. It has been felt that probably more correct ideas of 

 the nuclear masses are given by their characteristic appearance under 

 slight enlargement than by the identification of the limits of the area 

 in which the characteristic nerve-cells of the nucleus can be made out. 

 Comparison of the findings by these two methods has shown the varia- 

 tion to be very slight. 



In this reconstruction all the morphological characteristics of the 

 various nuclei have been preserved as long as the preservation was tech- 

 nically possible. This more intimate anatomy of the nuclei varies 

 undoubtedly in different brain-stems, but it has been thought of value 

 to present this finer morphology of one brain-stem, as it is only by this 

 means that the ultimate conception of the morphology of the nervous 

 system can be advanced. The grosser form of each nuclear mass is, 

 however, probably identical in all cerebro-spinal axes. 



Different nuclear masses have been modeled on the two sides of this 

 reconstruction. The left side shows only the individual collections 

 of nerve-cells which go to form the well-defined nuclei. The anterior 

 motor column is also modeled on this side, clearly cut away from the 

 central gray matter by the decussatio pyramidum. On this side, too, 

 the nuclei underlying the fourth ventricle are given in their relations to 

 each other. In contrast to this dissected left side of the model is the 

 more solid and less open right side. Here an attempt has been made to 

 show morphologically the transition of the indifferent gray matter about 

 the central canal of the spinal cord into the formatio reticularis of the 

 medulla. The external form of the formatio has been modeled on this 

 side, as has also the floor of the fourth ventricle. This presentation on 

 the one side of the surface markings of the ventricular floor and on the 

 other of the various nuclei which have surface representations permits 

 accurate comparison of the ventricular anatomy with the underlying 

 nuclear structure. 



In addition to the above grosser studies in development we have 

 directed our attention towards the structure and properties of the cell 

 and the development of individual tissues. 



The work of Professor Herbert M. Evans, on the behavior of the 

 somatic cells toward vital stains of the benzidine group, will have an 

 important bearing on cell classification and on our problems of histo- 

 genesis. Professor Evans has received several grants from the Rocke- 

 feller Institute and during the last year has published a considerable 

 body of his data. In collaboration with Werner Schulemann he exam- 

 ined several hundred dyes of known chemical constitution as regards 

 theu' biological behavior. These were all combinations of benzidine 



