ZOOLOGY AND BOTANY, MICfiOSCOPY, ETC 31 



judged from studies upon the germ-cells which have been made thus 

 far, sterility is a matter of the fundamental constitution of the organism. 

 It concerns bhe hearers of hereditary traits, the chromosomes. All of 

 the studies which have been made point to the conclusion that whatever 

 may be its nature, there is an 'incompatibility' existing between the 

 chromosomes of individuals of different species or varieties." 



Islands of Langerhans in the Human Embryo.* — T. Mironescu has 



made a study of the development of the islands of Langerhans in the 

 human embryo. He rinds that the first rudiments of these are developed 

 through the vascularization of epithelial buds or shoots arising from the 

 glandular ducts and glandular acini. The islands are only recognizable 

 by the arrangement of their cells and by their relation to the capillary 

 vessels. The author does not agree with Kuster that there is no increase 

 in the number of islands of Langerhans after early embryonic life ; from 

 his comparison of the pancreas of new-born infants with that of adults, 

 he infers that they increase in number even after birth, arising in the 

 same way as in the early life of the embryo. 



Development of the Sympathetic Nervous System in Mammals.f 

 A. Kuntz publishes an account of an investigation into the development 

 of the sympathetic nervous system in Mammals, undertaken to further 

 exact knowledge of the histogenesis of the sympathetic nervous system, 

 to establish the histogenetic relationships between the sympathetic 

 neurones and the neurones of the central nervous system, and to correlate 

 the sympathetic system with the other functional divisions of the nervous 

 system. His results are as follows : The sympathetic trunks arise as a 

 pair of cell-columns lying along the sides of the dorsal surface of the 

 aorta. In the early stages, medullary cells migrate from the neural tube 

 into the dorsal and the ventral nerve-roots. The cells, which migrate 

 into the ventral nerve-roots with similar cells which wander down from 

 the spinal ganglia, migrate peripherally along the spinal nerves. Some 

 of these cells deviate from the course of the spinal nerves, and, migrating 

 along the paths of the communicating rami, give rise to the sympathetic 

 trunks. The pre-vertebral plexuses arise as cell-aggregates lying along 

 the ventro-lateral aspects of the aorta in the posterior region of the 

 body. They are derived directly from the sympathetic trunks. The 

 cardiac plexus and the sympathetic plexuses in the walls of the visceral 

 organs are not derived from the sympathetic trunks, as has hitherto been 

 supposed, but have their origin in nervous elements which migrate from 

 the hind-bra in and the vagus ganglia along the fibres of the vagi. In 

 view of the relation of these plexuses to the vagi, the author calls them 

 " vagal sympathetic " plexuses. The cells migrating peripherally from 

 the cerebro-spinal system along the spinal nerves and the vagi are the 

 descendants of the " germinal " cells of His — that is, the " indifferent " 

 cells and the " neuroblasts " of Schaper-— therefore, they are homologous 

 with the cells giving rise to the neurones and the supporting elements in 

 the central nervous system. The cells migrating peripherally along the 

 spinal nerves and the vagi do not all take part in the development of 



* Arch. Mikr. Anat., lxxvi. (1910) pp. 322-8. 



t Joum. Comp. Neurol., xx. (1910) pp. 212-58 (18 figs.). 



