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 cm. 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 considei-ation 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. 1901 



Ueber den allgemeinen Bauplan des Tracheatensyncerebrums. 

 Arch. f. niicr. Anat., Bd. 65. 



Hilton, W. A. 1911 

 The structure of the nerve cells of an insect. Jour, conip. 

 neurol. Vol. 21, No. 4. 

 1912 



A preliminary study of the central nervous system of spiders. 

 Pomona jour. ent. Vol. IV, No. 3. 

 Saint Remi/. G. 1890 



Contribution a 1 "etude du cerveau chez les arthropods tra- 

 eheates. Theses a la Faculte des sciences de Paris. 

 (Contribtifion from ihc Znnlogical Laboratory of Pomona College.) 



