EMBRYOLOGICAL METHODS. 337 



of the ovum of the mouse ; fixation in FLEMMING'S weak 

 mixture,, sections stained with BEN DA'S iron htematoxylin) , 

 andAnat. Hefte, 1 Abth., viii, 1897, p. 476 (Babbit ; fixation 

 with liquid of Flemming or picro-sublimate with 2 per cent, 

 acetic acid) ; BONNET, ibid., ix, 1897, p. 426 (Dog ; fixation 

 in sublimate). 



Ave*. 



591. Superficial Examination. Instructions on this head 

 are given in FOSTKI; and BALFOUR'S Elements of Embryology. 

 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 011 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) . 



592. Gerlach's Window Method (Nature, 1886, p. 497 ; Journ. Boy. 

 Mic. 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 blasto- 

 derm will become placed underneath 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. iviss. Mik., iv, 3, 1887, p. 369. 



593. Preparation. Daring the first twenty-four hours of 

 incubation it is extremely difficult to separate the blastoderm 



22 



