292 Journal of Comparative Neurology. 



mice killed just after birth (body- weight unknown). The material 

 was preserved with Carnoy's mixture, and imbedded in paraffin 

 according to the usual procedure. The sections were cut 6 fj. 

 thick, and stained with a saturated aqueous solution of thionin 

 followed by 1% eosin in 70% alcohol. Besides these, sections 

 of the cord from man and the dog, treated with Weigert's 

 neuroglia stain, were used for comparison. 



For this investigation, the section of a region of the pons 

 was examined for the reason that owing to the small number of 

 nerve cells, the capillaries were there less abundant and easier 

 to observe. In this locality it is possible to follow various 

 stages of the migration of the proliferated cells of the capillary 

 wall into the brain substance. Around the capillaries a collec- 

 tion of nerve cells and neuroglia nuclei are clearly visible (Figs, 

 I, 2, 3, 5, 6). The nerve cells are well developed and the 

 protoplasmic processes, as well as the stainable substance in 

 the cytoplasm, may easily be demonstrated. In the case of the 

 neuroglia, however, the nuclei only are well defined, the cyto- 

 plasm being less differentiated and probably small in amount. 

 Although the nuclei of the neuroglia cells exhibit considerable 

 variation, a careful observation reveals that they are represented 

 by two distinctly characterized types. The following descrip- 

 tion aims to present the main characters of the two types just 

 mentioned. 



1. Size. As determined by the longest diameter, the 

 nucleus of the type "b" which measures 9.5/^, both in white 

 rat and mouse, is much longer than that of the type "a" which 

 measures 8.3 //, in the white rat and 7.4/^ in the mouse. Each 

 of the above diameters was obtained by taking an average from 

 the measurement of ten nuclei. 



2. Form. The external form of the nuclei is one of the 

 important features for a classification into two types. One form 

 (type a) of the nuclei presents a more or less circular or a 

 slightly oblong shape (Fig. 9), while the other (type b) shows 

 a more oblong or spindle form. A characteristic appearance 

 of this type "b" is that of a wavy outline of the nucleus or in 

 some cases an amoeboid form. 



