82 Journal of Comparative Neurology. 



human embryo lO mm. in length, its anlagc may be observed ; 

 its development falls therefore into the second month. His 

 further states that its development begins with the development 

 of the white rami communicantes. In a human embryo about 7 

 mm. in length, he describes short visceral branches, which leave 

 the anlagcn of the spinal nerves, a short distance beyond the 

 junction of the anterior and posterior roots, and at a point 

 where the spinal nerves reach the dorsal coelom border. These 

 branches grow in toward the aorta, and at this stage there are 

 as yet no cells in or on these rami. In tracing the develop- 

 ment of the sympathetic cells I shall follow the account given 

 by His, Jr. (11). The description given has reference chiefly 

 to observations made by him on chick embryos of the fourth 

 day. In cross sections of such embryos passing through a 

 spinal ganglion, small clusters of cells, the clusters numbering 

 2-4-10 cells respectively, are seen in the mesoblastic tissue be- 

 tween the point of junction of the anterior and posterior roots 

 and the aorta. The cells in these clusters differ in structure 

 and in their affinity to staining reagents from the surrounding 

 mesoblastic cells. 



They are of round, oval or polygonal shape, and have 

 large nuclei and nucleoli. They stain well in haematoxylin and 

 eosin, so that even under low power they may be differentiated 

 from the surrounding mesoblastic cells. The evidence seems 

 in favor of the supposition that these cells, which, as we will see, 

 are the germ cells of the sympathetic ganglia, do not develop 

 in loco, that is from the surrounding mesoblastic cells as was 

 formerly believed and has quite recently been asserted by Pat- 

 erson (12), but that they wander out from the spinal ganglia 

 as germ cells possessing this motile power. The origin of 

 these cells from the spinal ganglia was first suggested by Bal- 

 four (13) in his monograph on Elasmobranch fishes. Schenk 

 (14) and Birdsell arrived at the same results for birds and mam- 

 mals. Onody (15) has more recently, in a very comprehens- 

 ive paper, in which he gives the results of his observations on 

 the development of these structures, in the various classes of 

 vertebrates, reached a similar conclusion. 



