8 Papers from the Department of Marine Biology. 
be demonstrated to contain neurofibrils. Accordingly, several special 
methods of neurological technic were employed in preparing sections, 
including the Cajal, Paton-Bielschowsky, Golgi, Shunda, and Pal- 
Weigert methods. In no case were definite neurofibrils detected. 
Another structure or series of structures seen in the cyptoplasm of 
these cells was at first taken to be pathological in character, but when 
seen in the cells of all the skates examined (three Italian species at 
Naples,’ several English species, and four American species) it was 
concluded that no phenomena so constant in their presence could be 
abnormal. .The structures referred to are vacuoles, granules, and 
precipitates of a constant and specific structure found in the cyto- 
plasm of the cells and in the surrounding tissues. The cell in figure 5 
shows a few vacuoles in the cytoplasm and a large number of granules, 
particularly along the processes. Not all of the cells were found to 
show the vacuoles, and some showed many more than others, even in 
the same individual. A few typical vacuolated cells are shown in 
plate 3. Figures 6 and 7 are taken from a skate of the species Raia 
punctata, and figure 8 from a skate of the species Rava lems. 
The history of the vacuoles in the cells of Raia punctata appears to 
be as follows: In their earliest stages they are small and very numerous 
and are found principally in the larger masses of cytoplasm of the cell. 
Due to the distributed and often peripheral arrangement of the nuclear 
material, these larger masses of cytoplasm are usually in the central 
part of the cell. The vacuoles grow in size and become less numerous, 
indicating that a coalescence takes place to form fewer larger struc- 
tures. Figure 6 shows such a condition with one vacuole of consid- 
erable size and groups of much smaller ones. When thus increased in 
size they show at first an empty cavity which indicates the presence of 
some solution or soluble material in life. The cavity is lined with a 
fine membrane of delicate nature separating the cytoplasm from the 
contents of the vacuole. 
In a more advanced stage the vacuoles are all large, in some cases 
excessively large, and they are usually near the periphery of the cell- 
body. At this time it is often possible to see a slight acid-staining pre- 
cipitate in them having a definite fixation reticulum? (fig. 7). In what 
is taken to be a slightly later stage, figure 8, small round granules have 
made their appearance in the precipitate, and these granules grow in 
numbers and also in size. The number and size of the granules in ripe 
vacuoles varies greatly. Some vacuoles may have many small gran- 
ules. In one average-sized vacuole of a cell of Raza levis containing 
small granules, the number of granules was found to be 180 (the esti- 
mate of this number including a count of all the sections of the vacuole). 
1 The cells were observed in these species by Professor Ulric Dahlgren. 
2 With the exception of three figures especially referred to as text-figures, all figure references 
apply to the plates at the end of this paper. 
