DEVELOPMENT OF THE EMBRYO. 21 



drop of slightly warmed wax should be carefully laid upon the 

 embryo; and when the latter has become stiff, the whole surface 

 formerly turned to the slide should be covered with wax. To 

 prevent the two wax surfaces, between which the embryo now 

 lies, from again falling apart, as is often the case, a hot needle 

 must be several times run through the wax, though naturally 

 at some distance from the embrj'o. 



The serial sections were made by hand, without the aid of a 

 microtome, though this in the case of such small objects needs a 

 little practice to ba done easily. Tha cutting was made under 

 alcohol. Care should be taken, in cutting, that the place wdiere 

 the section is situated should be accurately marked. The 

 particular piece of wax is to be transferred with a needle from 

 the knife, which is laid flat on the slide. The section is now to 

 be treated with a drop of absolute alcohol ; and after removal of 

 the superfluous alcohol, a drop of oil of cloves should be added. 

 The latter is to be preferred to other means, inasmuch as it 

 does not easily evaporate, and the section may remain in it for 

 a longer time. The entire series of sections may now be placed 

 in oil of cloves. 



The removal of the wax is now brought about by the warm- 

 ing of the slide over a spirit-lamp. The warmed oil of cloves 

 soon acts as a solvent to the wax. After removal of the super- 

 fluous oil of cloves (the section may be easily taken out of the 

 warmed oil of cloves by means of a needle) the section can be 

 preserved in Canada balsam. 



The Ampliioxus begins to spawn in the first warm 

 days of spring, and so far as my observations went, as 

 early as the last days of March. The spawning goes 

 on through the whole summer. But it is, as we will 

 explain later on, dependent on the conditions of the 



