216 



M. IX AB A. 



tlie case of tlio monso, to demonstrate tlie distinction hotween tlie medul- 

 lîiry and (-(^rtical elements. In the preparations of the chromo-picro- 

 sidphnrie acid the mediilJa i« not coloured Ijrown ; this seems to he due 

 partly to the shortness of the interval during" which the emhryos 

 were exps^sed to the action of the reagent (1'/^ liours) and partly to the 

 presence of the [)icro-sul[)huric acid. To stain emhryos, I used a weak 

 solution of Kieinerdjerg's hematoxylin, as it gives the clearest and 

 most ditferentiated figures. With picrocarmine I also ohtained good 

 preparations of the suprarenal Ijodies of the young mouse. The 

 objects were stained in foto before imbedding in the celloidin paraffin. 

 In all cases I took pains to stain (h^eply and to cut sections as lliin 

 as possible. 



I am not C(uite snre of the age of the embryo, since I could not 

 observe any actual c<^-]inlation. After the method of Selenka, I separat- 

 ed the individuals of two sexes for from ten to fifteen days, then put 

 a ]inir together f >r a night, and separated them again the next morn- 

 ing. I connt(M:l the day of separation as the first day of gestation, the 

 next the second day. and so fu'th. Frcnn a number of preserved 

 embryos I determined the approximate size (from the tip of the head 

 to the root, of the tail) of the embryo in each stage as follows : 



nth day 3-4.5 mm. 



12th day 4.5-6 mm. 



13th day 6-8 mm. 



14th day 8-10 mm. 



15th day 10-12 mm. 



In cases of embryos older than this stage, I opened their ab- 

 domen as (piickly as possible before immersing them into the killing 

 fluid, and could not make any relialile measurement. 



Suprarenal ])odies of the Mouse, from the new- born 

 to the adult. — I commenced my study with the young mouse about 



