CHAPTER XXV. 275 



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. 



600. Special Cases. MITSUKURI (Journ. Coll. Sc. Japan, vi, 1894, 

 p. 229) fixes^mbryos of tortoises chiefly with picro-sulphuric jicid. 

 To study the blastoderm he removes the whole of the shell and as 

 much as possible of the albumen, marks the place where- the blasto- 

 derm lies with a hair, brings the whole, with the blastoderm upper- 

 most, into the fixative, and after a few hours cuts out the blasto- 

 derm 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^ujphuric^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., Abth. Morph., vi, 1892, p. 8) opens ova of 

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

 aceto-osmic acid with very little osmic acid) and lmrj^n^Jih^embry_os, 

 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 Tropido- 

 notus for twenty-four hours in Nowak's mixture, 112. 



BALLOWITZ (Entwickl. d. Kreuzotter, 1903, p. 19) first fixes seg- 

 ments 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 'Bourn's picro- 

 formol ( 110). 



See also PERENYI, 48, and Zool. Anz., 1888, pp. 139 and 196, 

 and other methods in early editions. 



Amphibia. 



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

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

 This may be done by putting them for two or three days into 1 per 

 cent, solution of chromic acid, and shaking well ; but ova thus 

 treated are very brittle, and do not afford good sections. A better 



18 2 



