272 CHARLES RUSSELL BARDEEN. 



esting description of the elements of the peripheral nerve plexus. 

 In this many nerve cells are found. Monti l has stained by the 

 Golgi method and described unipolar, bipolar and multipolar 

 cells lying both in and about the brain and nerve cords and in 

 the periphery next the musculature but she has not followed 

 their development. Bergendal 2 found in the central nervous 

 system of land planarians large ganglion cells, with very large 

 nuclei which stain lightly. 



I have made no extended attempt to stain the nervous system 

 of planarians by special methods. In and about the nerve-cords 

 and brain are scattered nuclei that stain very lightly and are 

 much larger than the nuclei of the fixed connective-tissue cells 



o 



(see Fig. 7, c, and compare with Fig. 4, /). These I have taken 

 to be the nuclei of nerve cells. The cell-body is usually difficult 

 to follow, but at times this may be seen sending off one or more 



m 



FIG. 7. Sections illustrating the development of the nervous system. Magnifica- 

 tion, 540 diameters. 



a. Large cell seen in the anterior ventral region of an embryo before the anlage of 

 the pharynx has appeared. 



b. Similar cells after the anlage has appeared. 



c. Early stage in the development of nerve fibers. 



d. Nerve cells in an adult individual. 



e. Row of nerve cells seen in a regenerating nerve cord. 



f. Nuclei of nerve cells undergoing direct division during regeneration of a new 

 brain. 



processes. At the stage of development in the embryo immedi- 

 ately preceding the formation of the permanent pharynx a few 

 large, palely staining cells may be seen in the anterior portion of 

 the ventral body wall. A cell of this kind is shown in Fig. 7, a. 

 I have not found these cells elsewhere in these embryos and 

 think it possible that they represent neuroblasts. I have tried to 

 find them in earlier stages of development without success. They 



1 " Sur le system nerveux des Dendroceles d'eau douce,'' Archiv. Ital. de Bi- 

 ologie, Vol. XXVII., 15, 1897. 



2 Zoologis cher A nzeiger, X., 218-224, 1887. 



