ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 443 



Ossification of Human Lower Jaw.* — Alex. Low confirms his 

 previous conclusion that each half of the lower jaw is developed in 

 membrane as a single skeletal piece — the dentary. Meckel's cartilage 

 takes only a slight part in the formation of the mandible, and does not 

 give rise to the condylar cartilage. 



Seal-embryos.f — H. W. Marett Tims gives an account of embryos 

 of Weddell's seal (Leptonychotes weddelli). He notes that the period of 

 gestation must be at least nine months ; that the muscles as a whole show 

 closer agreement with those of Trichechus than with those of Otaria ; and 

 that there is in the musculature some additional support for Mivart's 

 suggestion of a Lutrine origin for the Phocidaj. An interesting point 

 is the presence of what seems to be a vestige of an external ear in a very 

 early embryo. 



Development of Cranial Nerves in Birds.} — J. Belogolovvy con- 

 tinues his study of the development of the cranial nerves, lie describes 

 the histogenesis, and then applies his results to the much-discussed 

 problem of the metamerism of the head. His conclusions agree in the 

 main with those of Johnston. 



Development of Blindworm.§ — Ernst Meyer gives an account of 

 the development of Anyuis fragile, from the appearance of the pro- 

 amnion to the closure of the amnion, dealing particularly with the 

 brain, the notochord, and the hypochordal ridge. 



Oogenesis in Raiada3.||— J. Marechal and A. de Saedeleer discuss 

 the development of the first oocytes in Raia clavata, describing, for 

 instance, the synapsis or contraction of the chromatin mass. 



Segmentation and Gastrulation in Lamprey. H — L. Glaesner de- 

 scribes the segmentation of the egg in Petromyzon Jiuviatilis, the 

 formation of the blastula, with its micromeres and macromeres, the 

 gastrula- invagination, and the formation of the blastopore. 



The same subject is discussed by Marc de Selys-Longchamps,** who 

 has studied Petromyzon planeri. He describes the blastula, the incom- 

 plete gastrulation, the " notogenesis " or concrescence, the formation of 

 the mesoderm. He seeks to show that there is actual concrescence in 

 this type, and that gastrulation, notogenesis or concrescence, separation 

 of the mesoderm and of the axial structures, are not so much successive 

 phases in development, as concomitant processes. 



Development of Nephridium in Amphioxus.ft — Robert Legros 

 discusses this difficult problem. We cannot do more than indicate his 

 general conclusions. The nephridium, the excretory organ of the second 



* Journ. Anat. Physiol., xliv. (1909) pp. 83-95 (1 pi.). 



t National Antarctic Exped. (Nat. Hist.), v. (1910) pp. 1-21 (2 pis.). 



X Bull. Soc. Imp. Nat. Moscou, 1908, Nos. 3 and 4 (published 1910) pp. 325- 

 537 (1 pi.). 



§ Zeitschr. wiss. Zool., xciv. (1910) pp. 447-87 (2 pis. and 8 figs.). 



|| La Cellule, xxvi. (1910) pp. 7-24 (1 pi.). 



H Zool. Jahrb., xxix. (1910) pp. 139-90 (2 pis. and 31 figs.). 

 ** Arch. Biol., xxv. (1910) pp. 1-75 (3 pis.). 

 tt Anat. Anzeig., xxxv. (1910) pp. 5G1-87 (7 figs.). 



