270 EMBRYOLOGICAL METHODS. 



Fix for an hour and a quarter in a mixture of eight volumes of picrosulphuric 

 acid with one of 1 per cent, chromic acid. Wash out for twelve hours with 20 

 per cent, alcohol, and pass the ova very gradually through alcohol of 20, 28, 

 35. 43, 50, 60, and 70 per cent, strength, the last to be changed frequently 

 until all the picric acid is extracted. Before staining, the capsules of the ova 

 should be opened. Stain with borax-carmine or haeniatoxylin, and imbed 

 in paraffin. 



573. Kollmann's Method (see 40). 



574. Perenyi's Method (see 39). 



575. Pelagic Fish Ova (WHITMAN'S method ; Amer. Natural., xvii, 



1883, pp. 1204-5 ; Journ. Roy. Mic. Soc. (N.S.), iii, 1883, p. 912, and 

 Methods of Research, &c., p. 152). Fix by treatment first for five to ten 

 minutes with a mixture of equal parts of sea-water and | per cent, osmic 

 acid solution, and then for one or two days with a modified Merkel's solution 

 (due to Eisig), consisting of equal parts of 0'25 per cent, platinum chloride and 

 1 per cent chromic acid. Prick the membrane before transferring to alcohol. 

 Whitman found that the usual Merkel's fluid caused maceration of the em- 

 bryonic portion of the egg. Picrosulphuric acid causes the embryonic cells 

 to swell, and in many cases to become completely disorganised. The osmic 

 acid treatment is necessary in the case of segmenting ova because the 

 Merkel's fluid does not kill rapidly enough, so that eggs placed in it may 

 even pass through one or two stages of cleavage before dying. This fluid 

 arrests the process of blackening by the osmium, or will even bleach the ob- 

 jects if blackening has set in. (See also AGASSIZ and WHITMAN, in Proc. 

 Amer. Acad. Arts and Sciences, xx, 1884.) For later stages the authors re- 

 commend the method of Perenyi. 



576. Embryos of Teleostea (EABL-EUCKHAED, Arch. f. Anat. u. 

 Entw., 1882, p. 67). Fix in 10 per cent, nitric acid for fifteen minutes. 

 Remove the membranes, to avoid deformation of the embryos, and put the 

 ova back into the acid for an hour. Wash out in 1 to 2 per cent, solution of 

 alum for an hour, and harden in alcohol. 



Modification of this method by GOEONOWITSCH (see Morph. Jahrb., x, 



1884, p. 381). 



Tunicata. 



577. Distaplia. DAVIDOFF (Mitth. Zool. Stat. Neapel, ix, 1, 

 1889, p. 118) has some important observations on the fixation 

 of the ova of D. magnilarva. The best reagent is a mixture 

 of 3 parts of saturated solution of corrosive sublimate and 1 

 of glacial acetic acid. The ova to remain in it for from half 

 an hour to an hour, and be then washed for a few minutes in 

 water and brought through successive alcohols. Another 

 reagent, almost as good, consists of 3 parts of saturated solu- 

 tion of picric acid and one of gl;ici;il acetic acid, the objects 



