EMBRYOLOC.IOAL METHODS. 315 



into 90 per cent, alcohol with iodine added, and thence 

 gradually back into water, softens the shells in weak sodium 

 hypochlorite, washes and imbeds. 



642. Trematoda.— CoE {Zool. Jahrb., Ahth. Morph., ix, 1896, 

 pp. 563, 566), for the special study of the excretory system 

 of the Miracidia of Distuvmvi, kills with osmic acid, rinses 

 with distilled water, and puts for a couple of days into J per 

 cent, solution of silver nitrate. 



Egg-capsules may be softened with 5 per cent, caustic 

 potash and then burst open (Heckeet, Bibl. Zool., iv, 1889). 



643. Nematoda. — The ova of Ascaris megalocephala, a clas- 

 sical object of study, ai-e one of the most impervious things in 

 the animal kingdom. Years ago Pol related to me that he 

 had had ova segmenting right through absolute alcohol into 

 balsam. Bataillon {Arch. Entu'ickelnngsmech., 1901, p. 149) 

 has had ova showing living embryos after having been for 

 six months in liquid of Flemming, and found them to remain 

 alive for montlis after drying for 21. hours at 35 0., and 

 mounting in balsam, and for weeks in acids or alkalies. 



Doubtless the best fixative yet made known for ova fur- 

 nished with their capsules will be found to be that of 

 Oarnoy and Lebedn, § 80 {La Cellule, xiii, 1891, -p- QS). After 

 fixation the ova are carefully brought into 80 per cent, 

 alcohol, in which they are preserved. Imbedding should be 

 carefully done as recommended for the ova of Amphibia 

 (§ 603), but they ought not to retnain in the pure paraffin 

 for more than a minute to a minute and a half. But these 

 authors prefer the celloidin method. At least six weeks' 

 soaking in the different strengths of celloidin will be neces- 

 sary to ensure penetration. They stain with iron hasma- 

 toxylin. 



ZuE Steassen {Arch. EntwicTiehmgsmech., iii, 1896, p. 29) 

 fixes for twenty-four hours in a mixture of 4 parts 96 per 

 cent, alcohol and 1 part acetic acid, brings into pure alcohol, 

 stains with hydrochloric acid carmine, and brings gradually 

 into glycerin. 



Similarly Zoja {Arch. mile. Anat., xlvii, 1896, p. 218) and 

 Eei.angee {iUd., xlix, 1897, p. 309). Zoja stained with Bis- 

 marck brown and examined in dilute glycerin ; Erlanger 

 made paraffin sections and stained with iron haematoxylin. 



