CEANIAL SYMPATHETIC GANGLIA IN THE PIG 79 



peripherally from the neural tube and the spinal ganglia, in 

 early embryos of the pig, along the spinal nerves. As the writer 

 has shown in a series of earlier papers,'* the cells which thus 

 advance peripherally from the cerebro-spinal nervous system in 

 vertebrate embryos are the descendants of the 'germinal' cells 

 (Keimzellen) of His, viz., the 'indifterent' cells and the 'neuro- 

 blasts' of Schaper. Nearly all of the cells advancing peripherally 

 from the cerebro-spinal nervous system along the fibers of the 

 growing nerves, in the early stages of development, are cells of 

 the 'indifferent' type. These cells, as Schaper has pointed out, 

 may give rise to neuroblasts or to embryonic supporting cells, 

 or they may retain the capacity for further propagation by divi- 

 sion and give rise to new generations of 'indifferent' cells. Occa- 

 sional mitotic figures along the paths of the growing nerves 

 indicate that some of these cells have retained the capacity for 

 further propagation by division after they have become sepa- 

 rated from the cerebro-spinal nervous system. Among the cells 

 of the 'indifferent' type cells may occasionally be observed in 

 the paths of the growing nerves which are obviously neuroblasts. 

 These cells are characterized by a large cytoplasmic body which 

 may or may not be drawn out to a point at one side and a large 

 rounded or elongated nucleus showing little structure in the 

 interior except a well defined nucleolus (fig. 5) . 



As the cells of the 'indifferent' type advance peripherally along 

 the growing nerves the nuclei of many of them become distinctly 

 elongated or more or less irregular in outline. Nuclei may be 

 observed occasionally which are distinctly pyriform with the 

 broader end directed peripherally. Such modifications in the 

 form of the nuclei of the cells present in the growing nerves 

 during the early stages of development are, doubtless, correlated 

 with the processes involved in their peripheral displacement. 

 The nuclei which remain associated with the nerve-fibers, during 

 the later stages of development, become extremely elongated. 

 These, however, are the nuclei of the cells which are obviously 

 becoming differentiated to form the neurilemma. 



* See bibliography. 



