JOURNAL OF ENTOMOLOGY AND ZOOLOGY 95 
The magnitude of nerve cells in many forms seems to depend 
upon the number and extent of the processes. The size of the 
animal ought then to make a difference with that of the cells. 
In one of the Collembola recently studied, the animal was about 
1.5 mm. in length; the cells were about .002 mm. in diameter. 
In a large tarantula, one of 6 em. body length, the nerve cells 
were of several sizes. Some were .05 mm. by .03 mm. The 
smallest were about .02 by .015 mm. In a small spider of 1.5 
mm. length, the largest cells were less than .01 mm. in diameter 
(Fig. 1, F), while a young drassid of 1.5 mm. which was active 
but not mature, had nerve cells of about the same size (Fig. 
1,G). The cells in the last case appeared much like neuroblasts. 
The smallest functional nerve cells in the tarantula were a 
little larger than the neuroblasts of young forms, while the 
functional cells of a more mature spider were about the same 
size as these neuroblasts. The largest nerve cells of tarantula 
as compared with the largest of a small spider show the great- 
est contrast. 
In a consideration of the size of nerve cells in various 
animals it seems clear that although the larger organisms have 
the larger nerve cells, there are other factors than size of the 
animal and consequent length of the cell processes which deter- 
mine the magnitude of the neurones. 
REFERENCES 
Haller, B. 1904 
Ueber den allgemeinen Bauplan des Tracheatensyncerebrums. 
Arch. f. micr. Anat., Bd. 65. 
Hilton, W. A. 1911 
The structure of the nerve cells of an insect. Jour. comp. 
neurol. Vol. 21, No. 4. 
1912 
A preliminary study of the central nervous system of spiders. 
Pomona jour. ent. Vol. IV, No. 3. ? 
Saint Remy, G. 1890 
Contribution a 1’étude du cerveau chez les arthropods tra- 
chéates. Théses 4 la Faculté des sciences de Paris. 
(Contribution from the Zoological Laboratory of Pomona College.) 
