DIVISION OF OVUM (ECHINODERMATA) 287 



perience and I have studied the most various forms Helix is 

 by far the best subject, The best method for sections is that 

 last recommended by PLATNER (Arch. f. mik. Anat., xxxiii, 

 1889, p. 125). Fix for an hour in Flemming's strong chromo- 

 aceto-osmic mixture, and then for twenty-four hours in a fresh 

 quantity of the mixture diluted with three to four volumes of 

 water. (I can confirm the statement that a thoroughly long 

 fixation is absolutely necessary ; I generally used the un- 

 diluted fluid for twenty-four to thirty-six hours) . Platner then 

 washes out with water, brings the gland into alcohol, stains 

 for twenty-four hours in Apathy's modification of Heidenhain's 

 hsematoxylin, and washes out for some hours (twelve to twenty- 

 four) in the alcoholic bichromate solution, then washes out for 

 days in 70 per cent, alcohol in the dark, dehydrates, clears 

 with cedar oil, and imbeds in paraffin. The method followed 

 by me differed from this only in so far as I made sections 

 first, and stained on the slide with dilute Delafield's haema- 

 toxylin, or double-stained with haematoxylin followed by 

 safranin. 



In an earlier communication (Zeit. f. wiss. Mik., iv, 3, 1887, 

 p. 350) Platner had recommended Kernschwarz (see 195) 

 for staining. This gives very good results, but I think not so 

 good as haBmatoxylin. I do not think the Nebenkern stains 

 more electively, and the cell body does not seem to me to re- 

 main so transparent as with hsematoxylin. 



It is very important to supplement the results thus obtained 

 by study of the living cell. V. LA. VALETTE ST. GEORGE (Arch, 

 f. mik. Anat. } 1885, p. 584, and 1886, pp. 8 and 9) recom- 

 mends the use of an indifferent liquid such as serum, with 

 which a little gentian violet or dahlia is rubbed up. Perhaps 

 methylen blue may be found still more useful. If the cells 

 be killed by 1 per cent, acetic acid, the Nebenkern may be 

 stained (lightly) with dahlia or gentian. 



608. Nucleus of BALBIANI (' Noyau Vitellin," " Cellule Embryo- 

 gene ") (ZooL Anz., 1883, p. G59). This may be observed in the fresh state, 

 without the addition of any reagent, in the ova of some animals, amongst 

 others a great number of Arachnida and Myriapoda. It may be brought out 

 more distinctly by treating the ova with a mixture of equal parts of acetic 

 acid and 1 per cent, osmic acid, to which is added a little sodium chloride. 

 This mixture does not render ova so granular as pure dilute acetic acid. 



609. Division of Ovum (Echinodermata) (FLEMMING'S method, 



