1 6 THE AMPHIOXUS. 



beginning of the formation of the mesoblastic somites 

 up to the separation of three mesoblastic somites 

 were handled in a manner somewhat different from the 

 later ones, since they bear a different relation to the 

 reagents, owing to their greater richness in yolk 

 grannies. The embryos in sea- water under the cover- 

 slip (as far as the stage with three mesoblastic somites) 

 I killed by letting fall upon them a drop of half per 

 cent, perosmic acid, and on the appearance of a faint 

 brown colour I carefully added diluted glycerine. This 

 treatment should be regulated in such a manner that 

 first of all the brown colour does not become too deep, 

 which would cause the objects to be less transparent 

 than they should be. Secondly, care must be taken 

 that the form of the living object be fully preserved 

 without any shrinking taking place. This end can 

 be secured by keeping control over the alterations 

 under the microscope. Round those preparations 

 whose cover-slips were supported by wax feet, I put 

 110 varnish, so that I might be able to turn the objects 

 as I wished by shifting the cover-slip. Here, too, 

 the preparations kept for a year or more. Carmin 

 staining I found unnecessary, since, without its aid. 

 the clear granules are quite plainly to be distinguished. 



