570 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Preparing Blastoderm of the Chick. — C. Koller,* who has taken 

 np this subject in order to decide some disputed points in the embry- 

 ology of the chick, thus describes the method by which his prepara- 

 tions were made. 



The egg was subjected to the hatching method recommended 

 by Kolliker. At the proper time it was opened and its contents 

 carefully transferred to a glass ; as much of the albumen as pos- 

 sible being removed by the fingers or otherwise. In order to keep 

 a note of the exact direction in which it was wished to take the 

 sections, it was generally found necessary to make an indication on 

 the egg while still fresh, as in the earlier stages the appearances in 

 the surface of the yolk are rendered indistinct by the process of 

 hardening; to this end, Koller has been accustomed to insert with 

 forceps a small triangular pointed slip of paper into the yolk im- 

 mediately behind the germinal disk in such a way that it indicates 

 the extreme posterior margin of the blastoderm, and lies at the same 

 time in the median plane of the future embryo. The yolk is now 

 submitted for twenty-four hours to the action of a Jg- per cent, solu- 

 tion of chromic acid, and then for another twenty-four hours to one 

 of ^ per cent., and thus increasing the strength daily up to J per cent. 

 If the yolk is sufficiently hardened, the segment on which the blasto- 

 derm lies, together with the central mass, is detached with a fine 

 scalpel and immersed in distilled water for twenty-four hours to 

 remove the superfluous chromic acid. The yolk-membrane may be 

 very readily removed from the hardened germ without injuring the 

 latter. The blastoderm is stained entire with weak ammoniacal 

 carmine (length of staining twelve to twenty-four hours), then washed 

 by twenty-four hours' immersion in distilled water and placed in 

 absolute alcohol. It is ready for cutting in from one to two days. 

 After lying for a few minutes in oil of cloves it is imbedded in a 

 mixture of wax and oil. Sections are made by hand, using turpentine 

 to moisten the object. 



Preparing Embryos of Insects. f — In a paper on the embryonic 

 development of the BombycidEe, Dr. S. Selvatico describes the methods 

 he has made use of both for the preparation of entire embryos and for 

 sections. The species employed were Bombyx mori, Attacus Mylitta, 

 and Saturnia pyri. 



The eggs are first coagulated by plunging them in water at 75° C. 

 With a pair of fine-pointed forceps a small piece is removed from the 

 shell, in the case of Bombyx, without disturbing the underlying parts. 

 With a little care this is easily done, because on the eggs becoming 

 cold their contents are somewhat contracted and do not touch the 

 shell. In the case of Attacus and Saturnia the eggs have a harder 

 shell but are larger, and a razor was employed by the author. 



They are then hardened by leaving them for twelve hours in a 

 • 002 per cent, solution of chromic acid, and for twelve hours more in 

 a '005 solution. Then with a little care the shell can be easily 



* Arch. Mikr. Anat., xx. (1881) pp. 181-2. 

 t Journ. de Microgr., vi. (1882) pp. 220-1. 



