PHYSIOLOGY OF NERVOUS SYSTEM IN ARTHROPODS. 473 
ances is erroneous, as I am quite unable to stain the granules I 
took for nuclei, except those which manifestly belong to the 
basket-like fibres; neither can I find any such cells in the 
same organ in the pupa. I believe the rod-like fibres are either 
packets of primitive fibrillee, or medullated nerve fibres. In 
many specimens they exhibit the appearance of rods of 
granules. Viallanes says: ‘The external medullary mass in 
the Wasp, as in the Dragon-fly, consists entirely of punctate 
substance ;’ but in his later work on the brain of the Cricket, 
he adds: ‘When sections strongly impregnated with osmic 
acid are examined, the substance of this body is seen distinctly 
divided into three zones. The internal and external zones are 
strongly stained. Under low powers, two systems of striz 
may be observed, one normal to and the other parallel with the 
surfaces of the organ.’ This is a little disappointing from 
one who has apparently worked so long at the structure in 
question. 
The structure of the optic ganglion is as well described by 
Berger as by anyone since. In the intermediate layer the 
radial fibres are thinner, and make way for those parallel with 
the surfaces of the ganglion, and in young pupa the layer is 
almost entirely cellular. 
In the pupa the reticular substance is of small amount, and 
as development progresses it encroaches on the very thick 
cortex, which is correspondingly reduced in thickness, so that 
I conclude the reticular medulla originates from the cells of the 
cortex and from those of the intermediate layer, either by the 
great development of certain cell processes, which become 
nerve-fibres, or by the differentiation and fibrillation of the 
cells themselves. 
2. GENERAL PHYSIOLOGY OF THE NERVOUS SYSTEM IN 
ARTHROPODS. 
Very little is known of the special functions of the several 
parts of the nervous system in Arthropods. There is, however, 
a general similarity between the functions of the ventral chain 
