476 THE NERVOUS SYSTEM. 
4. The right half of the brain is in relation with the left 
half of the ventral chain, and vice versd. There is a complete 
decussation of fibres between the supra-cesophageal centres 
and the ganglia of the ventral chain, with which the infra- 
cesophageal ganglia must probably be included. 
This statement is supported by the experiments of Faivre on 
Dytiscus ; and by those of Yung and others on the Crustacea. 
Yung says, however, ‘ Each half of the brain (supra-cesopha- 
geal centre) acts upon the corresponding side of the body,’ 
although he also states that lesion of one of the lobes of the 
brain produces circus movements (mouvements de manége) 
from the injured to the sound side of the body. 
As all observers have stated that such movements occur, it 
appears to me that this entirely negatives Yung’s contention. 
Faivre accounts for the circus movements on the supposition 
that paralysis of the appendages of the uninjured side occurs, 
and this seems to be the case. 
Yung, on the other hand, evidently supposes that the lesion 
acts as a stimulus. This is most improbable, as Faivre has 
shown that even the slightest lesions give rise to rapid abroga- 
tion of function in all aquatic insects, from the destructive 
action of the water which acts upon the injured centre ; more- 
over, the same movements occur when the entire hemisphere 
is removed and in the same direction. This fact alone shows 
that Yung has arrived at a false conclusion. 
Anatomical investigations lead to the conclusion that the 
most extensive system of transverse commissural fibres exists 
in the supra-cesophageal centres, and that by far the greater 
portion of the conducting tracts decussate around the ceso- 
phagus; indeed, there is no evidence of the direct relation of 
the two halves of the supra-cesophageal portion of the brain 
with the corresponding halves of the metameral ganglia. 
5. The classical view that the dorsal tracts of the ventral 
cord are afferent and the ventral tracts are efferent is probably 
correct. The experiments of Faivre and Longet are in favour 
of this conclusion; but Vulpian, Lemoine [174] and Yung [179] 
could find no difference between the stimulation of the dorsal 
