ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 561 



from one ovum. A separation into several embryos begins after the 

 differentiation of the germinal layers. 



Changes in Cicatricula of Unfertilised Egg of Fowl.* — A. 

 Lecaillon points out that the cicatricula of unfertilised ova differs, 

 even before the egg is laid, from that of fertilised eggs. It shows 

 vacuoles in its peripheral region. These give rise to the " reseau de 

 Prevost et Dumas," which occupies the periphery of the germinal disk. 



Growth-period of Oocyte of the Fowl.t — Sonnenbrodt divides this 

 into a period of development and a period of growth in the stricter 

 sense. The former includes the time between the youngest stage of 

 the nucleus and the resting stage. During this period the chromosomes 

 are differentiated, they divide longitudinally, and a nucleolus arises. The 

 growth-period includes a change in the nuclear sap, the breaking up 

 of the nucleolus, the transformation of chromosomes into chromatin 

 strands, the breaking up of the strands into very fine granules, the 

 migration of the nucleus to the surface of the egg, the formation of 

 chromatic nucleoli, and the new formation of chromosomes. 



Development of Cornea in the Chick.J — Ernst v. Knape finds that 

 the development of the cornea in the chick is determined by three 

 factors — the ectoderm, the anterior vitreous body, and the mesoderm 

 cells. The ectoderm over the primordium of the eye is turned into the 

 corneal epithelium. In the anterior vitreous body a thickening arises — 

 the directive membrane of the cornea — which determines the direction 

 and limits of the immigration of mesoderm-cells that form the endo- 

 thelium. This directive membrane becomes the membrana Descemetii. 

 The part of the anterior vitreous body lying between the directive 

 membrane and the ectoderm forms in part the framework for the 

 immigrant mesoderm cells, from which the substantia propria arises, 

 and persists in part as Bowman's membrane. 



Influence of Size of Egg and Temperature on Growth of Erog.§ — 

 Robert Chambers experimented with eggs of Rana temporaria and 

 R. esculenta, seeking to determine how the initial size of the eggs and 

 the temperature affect the size of the developing embryos. He found 

 that small eggs have a tendency to develop rather faster, that large 

 eggs are more efficient in withstanding extremes of temperature, that 

 large tadpoles develop always from large eggs, that the size of the cells 

 of a tadpole or young frog is in direct relation to the size of the 

 examined individual, that therefore the size of the cells of an animal is 

 determined by the initial size of the egg from which it has developed. 



Three-year-old Tadpoles. || — W. Ahrend describes tadpoles of Pelo- 

 bates fuscus which have remained as tadpoles for three years. The 

 cause was mainly lack of sufficient food. "While caudal fin and branchial 

 respiration persisted, the spirally coiled gut was replaced by a short gut 

 like the adult type. 



* C.R. Soc. Biol. Paris, lxiv. (1908) pp. 1035-6. 



+ Archiv Mikr. Anat., lxxii. (1908) pp. 415-80 (4 pis.). 



J Anat. Anzeig., xxxiv. (1909) pp. 417-24 (4 figs.). 



S Archiv Mikr. Anat., lxxii. (1908) pp. 607-661 (9 figs.). 



II SB. Nat.Ver. Preuss. Rheinland, 1909, pp. 43-4. 



