CARPENTER: DEVELOPMEKT OF THE OCULOMOTOR NERVE. 175 



(h, unclassifiable type of development) by the development of ganglion 

 cells in situ in the third nerve (Dohrn, Beraneck, Rex, Reuter). 



None of the investigators who have observed the formation of the 

 ganglion in situ have advanced an opinion as to the source of its cells 

 with the exception of Dohrn, who gives evidence of their derivation 

 through migration from the wall of the neural tube. 



5. In all vertebrates, at an early stage in the development of the 

 of the ciliary ganglion, a connection, in the form of a communicating 

 ramus, is established between it and the ophthalmic branch of the 

 trigeminus. 



B. Observations. 



1. Methods. 



The two most satisfactory staining methods for the purposes of my 

 study proved to be the mixture devised by vom Rath for fixing tissues 

 and the Heidenhain iron haematoxylin stain. The vom Rath fluid used 

 according to Neal's procedure (see Neal, :03) has the very desirable effect 

 of differentiating neuroblasts and their growing processes. It colors 

 but slightly other cells of the neural tube (ependymal cells, spongio- 

 blasts and indifferent cells), and the same is true of its effect on the 

 cells of the mesenchyme. In preiiariug the fluid the formula used was 

 that given in 1895 by vom Rath~('95, p. 283) : — 



200 c.c. saturated solution of picric acid. 



1 grm. platinic chloride, dissolved in 10 c.c. water. 



2 c.c. glacial acetic acid. 



25 c.c. 2 per cent osmic acid. 



In this mixture, embryo chicks were allowed to remain for three days 

 or more, during which time the fluid was once changed. They were 

 then washed for a minute in two changes of methyl alcohol, and placed 

 for from twenty-four to forty-eight hours in a 0.5 per cent solution of 

 pyrogallio acid, which intensified the stain. From this reagent the em- 

 bryos were brought up slowly through the different strengths of alcohol 

 to absolute, then cleared in xylol, and embedded in paraffin. This treat- 

 ment rendered the material very brittle, and careful handling was neces- 

 sary in all operations subsequent to immersion in the fixing fluid. After 

 serial sectioning and fixation to the slides, no treatment for the further 

 staining of the tissues followed. The paraffin was dissolved in xylol, 

 and the sections were immediately mounted in xylol-balsam. The prep- 

 arations were allowed to dry uncovered, since the use of cover glasses 



