532 SUMMARY OF CURRENT RESEARCHES RELATING TO 



destined to form central nervous system, nephridial organs, larval 

 glands, &c. 



The author treats frogs' eggs, first with osmic acid for about twenty 

 minutes, and then transfers directly to the chrome platinum solution 

 (same strength as for pelagic eggs), for twenty-four hours. The eggs 

 are next placed in water and freed from their gelatinous envelopes 

 with needles and dissecting Microscope. They are next washed in 

 flowing water for two hours, then treated with alcohol and stained. 



Method of Killing Gephyrea.* — According to Dr. W. Apel the 

 only successful method of killing these animals, in an extended con- 

 dition, is by the use of hot water. The animal may be placed in a 

 vessel of sea-water, and the temperature gradually raised to about 

 40° C. ; or it may be seized by a pair of forceps while in a condition 

 of extension, and plunged for a moment into boiling water. This 

 latter treatment does not kill the animal, but renders it completely 

 limp, in which condition it should be cut open and then placed in 

 some hardening fluid. 



Macerating Mixture for central nervous system of vertebrates.f 

 — ^The following mixture, discovered by Landois, is recommended by 

 Dr. H. Gierke as an excellent macerating agent, especially for the 

 central nervous system of vertebrates : — Chromate of ammonium 

 5 grm. ; phosphate of potassium 5 grm. ; sulphate of sodium 5 grm. ; 

 distilled water 100 grm. 



Pieces of fresh tissues are left in this fluid from one to three, or 

 even four or five days, then transferred to a mixture (in equal parts) 

 of this fluid with ordinary ammonia-carmine (24 hrs.). 



Preparing the Hen's Egg. J — A very important addition to this 

 branch of technique has been made by M. M. Duval. 



First in importance are the methods of orientation. After the 

 appearance of the primitive streak, at about the twelfth hour of 

 incubation, it becomes easy to distinguish anterior, posterior, and 

 later regions in the blastoderm. Hitherto it has been a matter of 

 conjecture whether anterior and posterior regions became morpho- 

 logically defined at any considerable time before the formation of 

 this streak; and no one, before Duval, attempted to clear up the 

 question, simply because it appeared impossible to find any means of 

 orienting sections at an earlier date. Duval addressed himself to the 

 task of finding out the transformations of the blastoderm, which lead 

 up to the establishment of the primitive streak, and to this end he 

 was compelled to seek, first of all, for some reliable means of exact 

 orientation. 



Method of Orientation. — It was noticed by Balfour, and confirmed 

 by KoUiker, that the axis of the chick embryo lies constantly at right 



* Zeitschr. f. Wiss. Zool., xlii. (1885) pp. 459-529 (3 pis.). See this Journal, 

 ante, p. 73, and Amer. Natural., xx. (1886) p. 315. 



t Arch. f. Mikr. Anat., xxv. (1885) p. 445. Amer. Natural., xx. (1886) 

 p. 315. 



X Ann. Sci. Nat. — Zool., xviii. (1884) 208 pp. and 5 pis. See this Journal, 

 V. (1885) p. 615, and Whitman's 'Methods in Microscopical Anatomy and 

 Embryology,' 1885, pp. 163-7. 



