294 ALBERT KUNTZ 



ary sympathetic trunks increase in size and prominence the pri- 

 mary sympathetic trunks decrease until they finally disappear. 



The phenomena above described in embryos of the turtle are of 

 peculiar interest in view of the phenomena involved in the devel- 

 opment of the sympathetic trunks in the chick. In embryos of 

 the turtle, as in the chick, the earliest traces of the sympathetic 

 trunks are found along the lateral surfaces of the aorta. In em- 

 bryos of the turtle these formations do not give way completely 

 to secondary formations, as is the case in the chick, but early 

 break up to become aggregated once more during the later stages 

 of development. Again, in embryos of the turtle, cells do not 

 become aggregated at the median sides of the spinal nerves to form 

 ganglionic enlargements, as is the case in the chick, but deviate 

 from the course of the spinal nerves proximal to the origin of the 

 communicating rami and advance in irregular cellular tracts 

 toward the anlagen of the sympathetic trunks. In short, the phe- 

 nomena involved in the development of the sympathetic trunks in 

 the turtle seem to represent a generalized prototype of what has 

 become a highly specialized condition in birds. This does not 

 mean, however, that the sympathetic nervous system in turtles is 

 the direct ancestral type of the highly speciahzed sympathetic 

 nervous system in birds. The sympathetic nervous system in 

 turtles is, doubtless, a speciaUzation of a still more generalized 

 type in the ancient reptiles. The points of correspondence which 

 have been pointed out, however, seem to warrant the conclusion 

 that the sympathetic nervous system in birds bears a more or less 

 direct phylogenetic relationship to the sympathetic nervous sys- 

 tem in the ancestral type of reptiles. 



b. Histogenetic relationships. In my earlier papers I have 

 shown that the cells which migrate peripherally from the cere- 

 bro-spinal nervous system in embryos of mammals and of birds 

 are the descendants of the 'germinal' cells (Keimzellen) of 

 His; viz, the 'indifferent' cells and the 'neuroblasts' of Schaper. 

 They have the same genetic relationships, therefore, as the cells 

 which give rise to the neurones and to the neuroglia cells in the 

 central nervous system. The great majority of the cells which 

 migrate peripherally from the spinal ganglia and from the ventral 



