308 EMBRYOLOGICAL METHODS. 



lately using for fixation either Kleinenberg's solution or, for 

 young stages, Altmann's 3 per cent, nitric acid. Staining 

 and cutting as above. 



Aves. 



589. Superficial Examination. Excellent instructions on this 

 head are given in FOSTER and BALFOUR'S Elements of Embryo- 

 logy, to which, as it is certain to be in the student's hands, he 

 may be referred. What follows here is given merely as being 

 of more recent publication. 



If it be desired to observe a living embryo by transmitted 

 light, the egg should be opened under salt solution, as de- 

 scribed below. A little of the white is then removed through 

 the window, the egg is lifted out of the liquid, and a ring of 

 gummed paper is placed on the yolk so as to surround the 

 embryonic area. As soon as the paper adheres to the vitel- 

 line membrane, which will be in a few minutes, a circular 

 incision is made in the blastoderm outside the paper ring. 

 The egg is put back into the salt solution, and the paper 

 ring removed, carrying with it the vitelline membrane and 

 the blastoderm, which may then be brought into a watch- 

 glass or on to a slide and examined under the microscope 



(DUVAL). 



590. Gerlach's Window Method (Nature, 1886, p. 497; Journ* 

 Eoy. Hie. Soc., 1886, p. 359). Remove with scissors the shell 

 from the small end of the egg ; take out a little white by 

 means of a pipette ; the blastoderm will become placed under- 

 neath the window thus made, and the white that has been 

 taken out may be replaced on it. Paint the margins of the 

 window with gum mucilage, and build up on the gum a little 

 circular wall of cotton wool ; place on it a small watch-glass 

 (or circular cover-glass), and ring it with gum. When the 

 gum is dry, the cover is further fixed in its place by means 

 of collodion and amber varnish, and the egg is put back in 

 its normal position in the incubator. The progress of the 

 development may be followed up to the fifth day through the 

 window. 



A description of further developments of this method, with figures of 

 special apparatus, will be found in Anat. Anz., ii, 1887, pp. 583,- 609 ; see 

 also Zeit.f. wiss. Mik., iv, 3, 1887, p. 369. 



