TurRNER, Mushroom Bodies of the Crayfish. 349 
It would be claiming too much to hone that the above de- 
scription entirely solves the structure of the central body. 
Other fibers may enter into its composition of which the sec- 
tions studied give no clue, but it is thought that sufficient has 
been deciphered to show that the central body of the decapod 
crustacean brain is homologous to the central body of the 
insect brain. 
Among the worms, in both Lepidonotus (fig. 30, C. B.) 
and in Polynoe (fig. 33, C.B.) is found a structure which, judg- 
ing from its histological stucture and its location, I take to-be 
the homologue of the central body of the Crustacea and Insects. 
Procerebral Bridge. In the crayfish this is a median fibril- 
lar body which lies above (dorsad of) the central body (fig. 1, 
P.B.) and between the dorsal nidus and the median fibrillar 
mass. In both transverse and horizontal sections this body is 
horse-shoe shaped, with the horns directed towards the outside 
of the brain.' When viewed with alow power this seems to 
be an unpaired structure, but medium and high powers show 
that it is a paired structure; the two halves being connected by 
commissural strands (fig. 7, 8, P.B.), 
Histologically the procerebral bridge resembles the central 
body in being composed of a meshwork of fine fibrils. In size 
however it is much smaller. 
Both VIALLANES (’93) and KENnyon (96) express the belief 
that the branches and the nerves of the ocelli enter this body; 
but each admits that he has no conclusive proof of that assump- 
tion. Since this body is quite prominent in the Crustacea, 
where there are no ocelli, it seems conclusive that few if any of 
the fibrils of this body are derived from the nerves of the ocelli. 
As to the source of the fibrils I have no conclusive evi- 
dence, but there is much that leads me to believe that they 
originate in the numerous cells that environ the procerebral 
bridge. 
Both VIALLANES ('93) and Kenyon (’96) state that, in the 
insects, fibers connect the procerebral bridge with the central 
1 Tn one case out of many examined I found the horns directed inwards. 
