Smallwood and Rogers, Molluscan Nerve Cells. 59 



that there is the appearance of a thick membrane which seems to separate the 

 sphere from the cytoplasm. The clear region may be encroached upon and 

 occupied by radially arranged granules which vary in size. All stages in the origin 

 of the sphere may easily be seen in the same ganglion cell. In the frog these same 

 spheres have a nuclear origin, /. e., they are derived from the smallest bodies in 

 the nucleus. In the same manner as in the frog, arise the spheres in Tethys with 

 this difference, that the origin does not take place within, but without the nucleus. 

 The various stages in the development of the spheres are seen in the cytoplasm, 

 which may be compared to similar stages in the development of the spheres in the 

 ganglion cells of the frog. 



When the spheres attain a certain size, their destruction occurs as follows: 

 The central body becomes indistinct and the radial zone breaks up into large or 

 small pieces, finally becoming so small that they cannot be distinguished from the 

 cytoplasmic granules so far as their shape is concerned, but they retain their 

 avidity for stain, which gives them prominence everywhere. Some of the large 

 spheres do not go through these regular changes and are described as vacuoles 

 (Blaschen) with a thin wall and a clear center. In the transformation of the 

 sphere into a vacuole this stage corresponds to the term "Mitochondrien." When 

 the peripheral layer of the sphere is broken up into a number of loose threads the 

 term "Chondromiten" is applied to them. The largest spheres are as a rule the 

 oldest and arise out of the smallest, structureless globules (Kiiglchen) of the cyto- 

 plasm. These may be seen to grow and to differentiate themselves into a light 

 inner zone and a dark outer band. The larger the sphere, the more plainly the 

 granules, which finally assume a radial arrangement in the outer zone, appear. 

 The last stage in the formation of the sphere shows the central body assuming its 

 complete shape and size. 



Smallwood ('06) reported the presence of numerous vacuoles 

 in Haminea, Venus, Planorbis, Limax, Helix, Littorina, Melantho, 

 Montagua and Aplysia which were designated as lymph spaces. 

 A more extended study suggests that this term should be reserved 

 for the larger peripheral spaces" and that the term vacuoles more 

 correctly describes them. There is no definiteness about their 

 position or size in the cell (Fig. 7). Animals examined during 

 all seasons of the year show them to be present in living nerve 

 cells. 



From this review, we learn that the nerve cells of Nemerteans, 

 Annelida, Crustacea, Insecta and Mollusca among invertebrates 

 exhibit a highly modified cytoplasm. A sufficient number of 

 specimens have been examined in each of these great groups to 

 indicate the very general appearance of differential structures in 

 the cytoplasm other than fibrillar. In the introduction eleven 

 different terms are cited as having been given to this stainable 

 substance in the cytoplasm which of itself suggests that the prob- 

 lem is one of great difficulty; certainly a doubt must have existed 



