DEVELOPMENT OF THE EMBRYO. 19 



I will here describe somewhat more fully my manner of 

 procedure. By means of a little pipette the embryos are con- 

 veyed into little watch-glasses. The embryos I mention are 

 those which in the earliest stages lie inside the egg membranes 

 at the bottom of the glass, but as soon as they leave this mem- 

 brane rise up and swarm on the side of the glass which is 

 turned away from the light, and immediately beneath the 

 surface of the water. In this manner it is possible to have 

 several hundred embryos at once in a little watch-glass full 

 of sea-water. In the watch-glass are now added a few drops 

 (about ten) of a half per cent, solution of perosmic acid. The 

 quantity of the latter should be determined by the results of 

 experience, as also the duration of its action. Then the whole 

 contents of the watch-glass must be quickly poured into 

 a little cylindrical glass. We allow the embryos to settle at 

 the bottom of the latter, and then carefully pour away the 

 sea-water as far as possible. Then a sufficient quantity of 

 carmin must be poured in, and the embryo well covered with 

 it. The embryos which were to be used for cutting sections 

 were subjected to a very strong staining, for which about five 

 minutes are sufficient. The washing out of the carmin is done 

 in the glass itself. Water is poured in until the glass is full. 

 When the embryos have sunk to the bottom, and the water 

 is coloured by the carmin, as much as possible of it must be 

 thrown away ; and this process should be several times re- 

 peated, namely till the water shows no more sign of the car- 

 min. Then we must gradually add alcohol, first weak and then 

 stronger; at last this too must be removed, and the embryos 

 kept in absolute alcohol. The effect of the perosmic acid is 

 especially to be seen in the course of time in a considerable 

 darkening of the embryos, and this often to an extent that is 

 inconvenient. 



Before being preserved the object was always examined in 



