ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 515 



not the future hypoblast. The external one is a complex formed by 

 the future epiblast, plus an axial cellular band representing the marginal 

 zone and the yolk-plug of Amphibians. At the expense of this l)and 

 are formed the Vails of the archenteron, the notochord, and the meso- 

 blast. The canal of Lielierkiihn is a true archenteron ; its formation is 

 equivalent to gastrulation ; the notochord arises wholly and solely 

 from it. 



Development of Viper's Skull.* — Bernhard Peyer has studied the 

 development of the skull of Vipera aspis by the reconstruction method. 

 He cannot by any means confirm W. Kitchen Parker's view that the 

 development of the viper's skull made it easier to link together the 

 crania of Ichthyopsida and Sauropsida. The fact is that the snake's 

 skull is extremely differentiated, to be interpreted in terms of a genera- 

 lized Saurian type. As the author shows, the skull of a common lizard 

 (Lacerta) affords very useful clues to an understanding of the peculiarities 

 of the viper's. 



Development of Parietal Eye in Reptiles.f — M. Nowikoff finds 

 that the epiphysis arises quite independently of the parietal eye, that it 

 is quite like the latter both in origin and in structure, and that it is in- 

 nervated like the latter from the commissura habenularis. He supports 

 Dendy's view that the two parietal organs in Cyciostomes and in Sphenodon 

 represent two lateral organs which have been secondarily shunted into 

 the middle line. The mode of innervation suggests that the parietal 

 eye is the right and the epiphysis the left member of the pair. Nowikoff 

 goes even further and regards the parietal eye as a ha If -developed lateral 

 eye and the epiphysis as a half -developed parietal eye. Morphologically 

 the two structures represent a pair of degenerate lateral optic organs 

 arising behind the ordinary eyes. 



6. Histology. 



Measurements of Chromosomes. J — C. F. U. Meek has measured 

 the chromosomes in a number of complexes, selecting material representa- 

 tive of the varions subdivisions of the animal kingdom. 



Some of his general conclusions are the following. In metaphases 

 the relative positions of chromosomes in the equatorial plane are arbitrary. 

 Ordinary chromosomes are composed of cylindrical rods with rounded 

 ends ; each spermatogonia! and secondary spermatocyte chromosome 

 consists of two such rods, and each primary spermatocyte of four, and 

 the same composition occurs in the corresponding stages in the female. 

 The somatic chromosomes are identical with those of the germ-cells. 

 The rods appear to be indivisilile units, which are separated in the various 

 mitoses, but never individually bisected. The loss in chromatin volume 

 caused by mitosis is compensated by growth in the intervening resting 

 stages, when granules double their volume and split upon the linin 



* Morphol. Jahrb., xliv. (1912) pp. 563-621 (3 pis. and 22 figs.). 



t Verb. VIII. Interuat. Zool. Kougress zu Graz., 1910 (1912) pp. 384-8. 



X Phil. Trans., Series B, cciii. (1912) pp. 1-74 (5 pis.). 



