ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 33 



independent of each other, but become united later by longitudinal 

 commissures. The primary sympathetic trunks reach their maximum 

 development during the course of the sixth day, after which they 

 decrease in size until they disappear. These results agree essentially 

 with those of His, jun., but the author finds that the cells giving rise 

 to the sympathetic trunk are not derived exclusively from the spinal 

 ganglia, as His supposes, but that they are derived wholly or in part 

 from the neural tube. Medullary cells migrate from the neural tube 

 into the ventral roots of the spinal nerves. 



With similar cells which wander out from the spinal ganglia, these 

 cells migrate peripherally along the spinal nerves. At a point a little 

 above the level of the aorta, cells deviate from the course of the spinal 

 nerves, and migrating towards the aorta, give rise to the primary sym- 

 pathetic trunks. As migration proceeds, the cells which deviate from 

 the course of the spinal nerves no longer wander into the primary sym- 

 pathetic trunks, but become aggregated at the point of origin of the 

 communicating rami, and give rise to the rudiments of the secondary 

 sympathetic trunks. The pre-vertebral plexuses arise as cell-aggregates 

 lying along the ventro-lateral aspects of the aorta from the supra-renals 

 posteriorly. They are derived directly from the primary sympathetic 

 trunks. The ganglion of Reinak arises as an oval cell-column lying in 

 the mesentery just dorsal to the rectum. It arises from cells which 

 migrate ventrally from the hypogastric plexus. The cardiac plexus and 

 the sympathetic plexuses in the walls of the visceral organs arise from 

 cells which migrate from the hind-brain and the vagus ganglia along 

 the fibres of the vagi. In the posterior region of the intestine the 

 myenteric and the submucous plexuses probably receive some cells from 

 the ganglion of Reinak. The cells, which migrate from the neural tube 

 and from the cerebro-spinal ganglia along the spinal nerves and the 

 vagi, are the descendants of the " germinal " cells of His, the " indif- 

 ferent" cells or "neuroblasts" of Schaper. They are, therefore, 

 homologous with the cells which give rise to the neurones and the 

 neuroglia cells in the central nervous system, and the sympathetic 

 neurones are homologous with the afferent and the efferent components 

 of the other functional divisions of the peripheral nervous system. 

 These observations agree with the author's observations on mammalian 

 embryos. Certain morphogeuetic differences exist between the develop- 

 ment of the sympathetic nervous system in Birds and Mammals, and 

 these the author interprets as indicating that the sympathetic system has 

 departed more widely from the ancestral type in Birds than in Mammals. 



Duplicity in Chick Embryos.* — Chas. H. O'Donoghue describes 

 three specimens of duplicity, worthy of note, as they are in other respects 

 practically normal. In the three cases the two halves are practically 

 equal in development, a condition called by Saint Hilaire autositic, 

 although the extent to which fusion occurs differs considerably, varying 

 from complete anterior fusion to complete independence. Two were 

 syncephalic monsters, the third showed two apparently independent 

 embryos, which were very closely approximated in their cranial portions, 



* Anat. Anzeig., xxviii. (1910) pp. 530-6 (4 figs.). 

 Feb. 15th, 1011 d 



