ii6 Journal of Comparative Neurology and Psychology. 



MANN ('99), working on selachians, confirms the findings of Balfoi'^r, 

 in their essential features. 



A brief summary of the literature embodies the following points: 

 (i) The cells from which the sympathetic arises, probably come orig- 

 inally from the spinal ganglia, as shown particularly by Balfour ('78), 

 ScHENK and Birdsell ('79), Onodi ('86), and His, Jr. ('97), Pater- 

 son ('91) being the most recent investigator to hold to the mesoblastic 

 theory. {2) In elasmobranchs, the sympathetic begins with the devel- 

 opment of the ganglia, which arise as cellular outgrowths on the spinal 

 nerves. These gradually are removed from the nerves, retaining, how- 

 ever, fibrous connections, which constitute the rami The commissures 

 arise later, probably as outgrowths from the sympathetic ganglia. (3) In 

 mammalia and in aves, the sympathetic appears first as a continuous 

 longitudinal cord, which later is joined by rami communicantes, arising 

 as outgrowths from the spinal nerves. At the points where the rami 

 join the cord, ganglia develop, while the intervening portions of the 

 cord remain as commissures. (4) The collateral sympathetic arises as 

 outgrowths from the sympathetic cord. (5) A portion of the sympathetic 

 anlage has, during its development, very intimate relation with the adren- 

 als. (6) From an embryological as well as from an adult morphological 

 and physiological stand-point, the sympathetic system is best consider- 

 ed as an integral part of the whole nervous system and not as a struct- 

 ure that is to any considerable extent distinct or separable from the 

 rest of the nervous system. 



My own observations upon the development of the sympa- 

 thetic nervous system have been confined mainly to the deriva- 

 tions of the ganglia, their commissures, and the rami communi- 

 cantes. The observations were made upon toad and frog em- 

 bryos, and were limited to the region posterior to the vagus 

 ganglion. Graphic reconstructions were made from serial trans- 

 verse parafifine sections, supplemented by actual dissections. 

 For the sake of clearness, a general statement is given before 

 proceeding to the description of particular stages of develop- 

 ment: 



(i) The sympathetic system between the vagus ganglion 

 and the second spinal nerve, in the animals studied, appears to 

 arise from cells scattered in the mesoblast of the region where 

 the future sympathetic cord is to lie. A portion of these cells 

 gradually becomes aggregated to form a cord (Fig's. 2, 7, and 



