Turner, Mushroom Bodies of the Crayfish. 353 
much the optic chiasm of the vertebrates. I have not been 
able to identify this tract in Branchipus. 
Dorso-lateral Optic Tract. This tract arises from the lateral 
portion of the dorsal nidus and passes in a ventrally directed 
convex curve (latero-ventrad) almost to the inner mushroom 
nidus; there it branches, a portion going to the outer tract of 
the optic nerve and the remainder passing downwards (ventrad) 
into the neighborhood of the stalks of the mushroom body 
where I lost it. There is much which leads me to believe that 
the forking of this tract is caused by each fiber dividing into 
two branches; but the evidence at hand is not conclusive (fig. 
St i::); 
Optico-mushroom Tract (figs. 2, 5, 20, 23, O.M.T.). This 
is a prominent tract which may be readily traced fromthe inner 
(mesal) portion of the optic nerve to the optic chiasm (fig. 2, 
7). There it branches, one branch decussating through the 
optic chiasm, the other making a sharp turn (fig. 7) and passing 
along with the decussating tract from the opposite side to the 
stalks of the mushroom bodies (fig. 2). There it branches, one 
branch passing into the optic lobe and one branch into the ol- 
factory lobe (fig. 7, 20). 
Fibers which originate in the outer mushroom nidus enter 
the optic lobe along with the fibers of the optico-mushroom 
tract. For a long time I was inclined to believe that the fibers 
arising from the outer mushroom nidus branched upon reaching 
the optic lobe, one fork passing into the lobe and the other 
passing into the optico-mushroom tract, but I have not been 
able to demonstrate this. 
' This optico-mushroom tract corresponds to one of the 
optic tracts described by KrizcEr (’88). Ina figure he shows 
that the tract does not decussate through the optic chiasm, but 
terminates in the mushroom body of the same side. 
Optico-oesophageal Tract. This is a small tract which passes 
from the inner portion of the optic nerve to the oesophageal 
collar of the same side. 
Although a small tract, yet in methylen-blue preparations 
