EMBilYOLOGICAL METHODS. 299 



Reptilia. 



600. General Directions.— The methods described above for 

 birds are applicable to reptiles. During the early stages 

 the blastoderm should be hardened in situ on the yolk ; 

 later the embryo can be isolated, and treated separately. 



BoHM and Ofpel {Taschenhuch, 1900, p. 186) remove the 

 shell under salt solution, fix in sublimate with 20 per cent, 

 acetic acid, or in Lo Bianco's chromo-sublimate (§ 72), then 

 remove the blastoderm and bring it into alcohol. 



601. Special Cases. — Mitsukuki {Journ. Coll. 8c. Japan, vi, 

 1894, p. 229) fixes embryos of tortoises chiefly with picro- 

 sulphuric acid. To study the blastoderm he removes the 

 whole of the shell and as much as possible of the albumen, 

 marks the place where the blastoderm lies with a hair, 

 brings the whole, with the blastoderm uppermost, into the 

 fixative, and after a few hours cuts out the blastoderm and 

 further hardens it by itself. Young embryos generally 

 adhere to the shell and can, therefore, be fixed in a piece of 

 it made to serve as a watch-glass, then after half-an-hour 

 can be removed from it and further hardened alone. If the 

 embryonal membranes have been formed, the shell may be 

 scraped away at some spot and there treated with picro- 

 sulphuric acid until a small hole is formed ; then by working 

 away from this spot, by means of scraping and dropping 

 acid on to it, the whole of the shell may be removed. 



Will {Zool. Jahrb., Ahth. Morpli., vi, 1892, p. 8) opens 

 ova of Platydacfylus in the fixative (chiefly chromic acid, or 

 chromo-aceto-osmic acid with very little osmic acid) and 

 hardens the embryos on the yolk ; so also for Cistudo and 

 Lacerta (1893 and 1895). Mehnert [Anat. Anz., xi, 1895, 

 p. 257) does not approve of these methods ; for his own see 

 3Iorph. Arh. Schwalbe, i, 1891, p. 370. 



Geehaedt [Anat. Anz., xx, 1901, p. 244) fixes ova of 

 TropidonottLS for 24 hours in Nowak's mixture, § 112. 



Ballowitz [Entwickl. d.Kreuzotter, 1903, p. 19) first fixes 

 segments of the uterus, each containing an ovum, for 1 or 2 

 hours, then tears them open with forceps, isolates the ova, 

 and puts them into fresh fixative, and thence into alcohol of 

 40 per cent. 



