ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 283 



measuring 10 by D'5 mm. The particular interest of the stage is that 

 the primitive streak area co-exists with, though independent of, a 

 primitive knot whose interior is penetrated by the archenteric or gastrula- 

 cavity. The mere fact of the co-existence of the streak with the knot 

 at this stage necessitates some reconsideration of the morphological 

 relationship of the mammalian primitive streak to the process of gas- 

 trulation. 



Development of Vertebral Column of Penguin.* — H. Mannich 

 gives a careful account of the development of the backbone in Eudyptex 

 chrysocome, and the most interesting general result is a demonstration of 

 the large number of primitive reptile-like skeletal peculiarities, which 

 are much more marked in this isolated and ancient stock than in most 

 other birds. 



Development of Beak of Penguin. t — M. Lewin describes the 

 development of the anterior part of the skull in Eudyptes chrysocome. 

 He notes inter alia that derivation from flying birds is suggested by the 

 air-spaces which extend from the nasal chamber into the beak on to the 

 middle of embryonic life, thereafter dwindling and eventually disappear- 

 ing. But the divergence from the main Carinate stock must have been 

 early, as is suggested by the persistence of various Saurian features, e.g. 

 the long-continued separateness of the bones of the skull, and the nature- 

 of the lachrymal canal. 



Development of Corpus Vitreum.J — M. von Lenhossek has studied 

 this in rabbit, cat, ox, and man. The vitreous body as a Avhole in a 

 product of the lens, and therefore of ectodermic origin. Its cells are 

 compared to the ependym-cells of the central nervous system. The 

 fibrillar vitreous substance forms a unified coalescent framework ; the 

 relations of its fibrils to the retina are quite secondary. The membrana 

 hyaloidea is derived from the retina, and has nothing genetically to do 

 with the vitreous body. The capsule of the lens is a cuticular forma- 

 tion from the cells of the lens-vesicle. 



b. Histology. 



Nature of the Centrosome.§ — D. X. Voinov has studied the centro- 

 some, particularly in the V-form which it exhibits in the spermatocytes 

 of various insects. He concludes that the centrosome is a real structure, 

 a true cellular organ, possessing some degree of autonomy, and some 

 persistence of form apart from structural changes in the cells. It grows 

 and develops by its own activity. It is transmitted by division from 

 one cell-generation to another, and may exhibit a precocity of develop- 

 ment — the V-form — in certain cases of rapid cellular transformation. 



Laws of Division. || — P. A. Dangeard recalls the law of Hertwig, 

 that the two poles of the nuclear spindle lie in the direction of the 

 largest masses of protoplasm, and the law of Pfliiger, that the nuclear 

 spindle is orientated in the line, of least resistance. 



* Jenaische Zeitschr. f. Naturwiss., xxxvii. (1902) pp. 1-40 (1 pi.). 



t Tom. cit., pp. 41-82 (2 pis. and 5 figs.). 



% 'Die Entwickelung des Glaskorpers,' Leipzig, 4to, 106 pp., 2 pis., and 19 figs. 



§ Arch. Zool. Exper., i. 4th series (1903) Notes et Revue, No. 2, pp. xvii.-xxiv. 



|| Comptes Rendns, exxxvi. (1903) pp. 163-5. - 



