EMBRYOLOGY 391 



strong liquid of Flemming. but the ova must then be bleached 

 with chlorate of potash (§ 611). 



Lenssen {La Cellule, xiv, 1898, p. 428) fixes ova of Hydatina 

 with sublimate for twenty seconds. 



863. Turbellaria. Gardiner {Journ. of Morph., xi, 1895, 

 p. 158) finds the best fixative for ova of Polychoerus is a mixture 

 of equal parts of absolute alcohol and glacial acetic acid. 



Bresslau {Zeit. vciss. ZooL, Ixxvi, 1904, p. 219) fixes Mesosto- 

 midrC with summer-eggs in Tellyesniczky's mixture (either cold 

 or warmed to 60° or 70° C.) for ten to twelve hours, and washes 

 out for the same time. He incises winter-ova at one pole, fixes 

 and brings into alcohol of 95 per cent., then makes an incision 

 at the other pole, and imbeds in paraffin through cedar oil. In 

 the paraffin, slices of the shell may be removed with a scalpel, 

 and the ova re-imbedded when sufficiently shelled. 



Van der Stricht {Arch. Biol., xv, 1898, p. 370) finds that 

 ova of Thysanozoon will only cut well when they have been not 

 more than two minutes in absolute alcohol followed by chloroform 

 and paraffin as used by Carnoy and Lebrun, § 825. 



See also, for Polyclads, Francotte, Arch. Zool. Exper., vi, 

 1898, p. 196 ; and, for fresh-water Planaria, Iijima, Zeit. wiss. 

 ZooL, xl, 1884, p. 359. 



864. Cestoda (v. Beneden, Arch. Biol., ii, 1881, p. 187). Ova 

 of Tcenia in which a chitinous membrane has formed around the 

 embryo are impervious to reagents. They may be put on a slide 

 with a drop of some liquid and covered. Then, by withdrawing 

 the liquid by means of blotting paper, the cover may be made 

 to gradually press on them so as to burst the membranes, and the 

 embryo may then be treated with the usual reagents. 



Haswell {Quart. Journ. Micr. Sci., liv, 1909, p. 417) fixes ova 

 of Temnocephala in " sublimate alcohol," brings them into 90 

 per cent, alcohol with iodine added, and thence gradually back 

 into water, softens the shells in weak sodium hypochlorite, washes 

 and imbeds. 



865. Trematoda. Coe {Zool. Jahrh., Abth. Morph., ix, 1896, 

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

 Miracidia of Distomum, kills with osmic acid, rinses with distilled 

 water, and puts for a couple of days into ^ per cent, solution of 

 silver nitrate. 



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

 and then burst open (Heckert, Bibl. ZooL, iv, 1889). 



Dr. W. Rees Wright {Annal Trop. Med. and Par., 1927) uses 

 Bouin and acetic alum carmine or Heidcnhain for redige and 

 cercarise. 



866. Nematoda. The ova of Ascaris megalocephala, a classical 

 object of study, are one of the most impervious things in the 

 animal kingdom. Years ago Fol related to Lee that he had had 



