14 THE AMPHIOXUS. 



get a clear understanding with regard to the chief axis 

 reaching from the upper (animal) to the lower (vege- 

 table) pole. 



Kleinberg's picric sulphuric acid proved itself 

 extremely useful for the preservation of the segmen- 

 tation stages, since the form and direction of the seg- 

 mentation elements undergo 110 change through its 

 employment. 



I set a row of little watch-glasses which were almost filled 

 with picric sulphuric acid. Into these, so soon as a new char- 

 acteristic stage began, a little pipette was emptied full of indi- 

 viduals of exactly the same ages. This row of little watch- 

 glasses which, without any break, contained the successive seg- 

 mentation stages, was subjected to a farther process the next 

 morning. In accordance with Kleinberg's well-known instruc- 

 tions, the objects were washed in alcohol to remove the picric 

 sulphuric acid, and were finally preserved in the same some- 

 what diluted. From this row of segmentation stages which I 

 had preserved, I was able, after the lapse of a year, to make 

 preparations of a suitable kind. It is possible from these glasses, 

 by means of a pipette, to bring up a sufficient quantity of 

 .segmentation stages ; and these, freshened with glycerine, yield 

 preparations which very closely represent the living object. I 

 .am acquainted with no object from which can be obtained so 

 .suitable demonstrative preparations. 



The employment of stains I consider superfluous. In 

 these early stages, when the granules of the yolk are 

 still very numerous, osmic acid turns the elements far 



