378 EMBRYOLOGY 



REPTILIA 



822. General Directions. The methods described above for 

 birds are apphcable 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 Oppel {Taschenbuch, 1900, p. 186) remove the shell 

 under salt solution, fix in sublimate with 20 per cent, acetic acid, 

 or in Lo Biakco's chromo-sublimate (§ 77), then remove the 

 blastoderm and bring it into alcohol. 



823. Special Cases. Mitsukuri {Journ. Coll. Sc. 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 w^here 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. Morph., vi, 1892, p. 8) opens ova 

 of Platydactylus in the fixative (chiefly chromic acid, or chromo- 

 aceto-osmlc 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 Morph. Arb. Schwalbe, i, 1891, 

 p. 370. 



Gerhardt {Anat. Anz., xx, 1901, p. 244) fixes ova of Trojyido- 

 notus for twenty-four hours in Nowak's mixture, § 117. 



Ballowitz (Entzvickl. d. Kreuzoiter, 1903, p. 19) first fixes 

 segments of the uterus, each containing an ovum, for one or 

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

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

 40 per cent. 



Nicolas {Arch. Anat. Mic, 1900, p. 457) finds the best fixative 

 for ova of the slow-worm, as for other large ova, is Bouin's 

 picro-formol (§ 115). 



See also Perenyi, § 45, and Zool. Anz., 1888, pp. 139 and 196, 

 and other methods in early editions. 



AMPHIBIA 



824. Preliminary. In order to prepare ova for section-cutting, 

 it is essential to begin by removing their thick coats of albumen. 



