EMBEYOLOGI-CAL ME'J'HODS. 295 



(embryos of the sheep best fixed in Carney's acetic acid, 

 alcohol, and chloroform, § 85) ; Winiwaetee, Arch. Biol., 

 xvn, 1900, p. 39 (mixture of 50 parts saturated sublimate 

 in salt solution, 50 parts alcohol, 20 of 1 per cent, platinum 

 chloride, and 5 of acetic acid) ; Sped, Encycl. Mih. Techn., 

 1910, p. 353 (cornua of Gavia fixed for 12 to 24 hours in 

 sublimate, and put into 0-5 per cent, osmic acid till light 

 brown, then into iodine alcohol, in which the osmium is 

 reduced) ; Widakowich, Zeif. wiss. Zool, xciv, 1909, p. 243 

 (J/ms rattus, fixation in Zenker's mixture, or 2 parts of 

 alcohol of 80 per cent, with 1 of formol ; also instructions 

 for dissection). 



Aves. 



693. Superficial Examination. — Instructions on this head are 

 given in Fostee and Balfouk's Elements of Embryology. The 

 following is 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 ai'ea. 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 

 i-ing 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). 



594. Gerlach's Window Method (Nature, 1886, p. 497). — 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 just 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. 



