The Eetina and Optic Ganglia in Decapods, especially in Astacus. 53 
itself. To carry out such a line of research to auything approaching 
completeuess would, however, extend the present investigations far 
beyond what I originally set as their limits, and I content myself, 
therefore, with a few brief comparisons , in tbe belief that they 
will indicate tbe more important conclusions to whicb such studies 
would lead. 
For matters of comparison witb tbe crayfisb one of the most 
instructive crustaceans is Branchipus. The optic ganglia of tbis 
animal bave already been carefully studied, especially by Claus (86), 
and there is little to add to bis extended account of tbem. As can 
be seen in Figure 28 (PI. 1), tbe ganglionic mass in Branchipus 
consists of two portions; tbe distal of these is tongue-sbaped (I), 
receives tbe retinal fibres, and gives off from its proximal face fibres 
that connect it witb tbe second or proximal portion; tbis (II) is 
considerably elongated and tapers proximally into the optic nerve 
[n.opt], These two masses are not only connected by bundles of nerve 
fibres, but tbey are actually confluent at their dorsal extremities {x). 
In spite of repeated attempts, I never succeeded in obtaining 
good preparations of tbe optic ganglia in Branchipus stained eitber 
witb methylen blue or by tbe Golgi metbod, and I am, tberefore, 
obliged to depend entirely upon ordinary preparations for tbe finer 
anatomy of tbese Organs, 
Tbe distal ganglion in Branchipus bas many resemblances to tbe 
first optic ganglion in the crayfisb. Like the latter, it is dome- 
shaped with its convexity facing tbe retina. It is composed of two 
layers, a distal one of nuclei .closely set and a proximal one of 
»Punktsubstanz«. In position tbe nuclear layer corresponds to tbe 
two nuclear layers and tbe fibrous layer in Astacus^ for the single 
layer in Branchipus extends from tbe distal surface of tbe ganglion 
.to tbe »Punktsubstanz«. It is also penetrated by tbe retinal fibres as 
tbe three layers in Astacus are. If these tbree layers in Astacus 
are equivalent to tbe single one in Branchipus^ the condition in the 
latter probably represents tbe more primitive one, an assumption 
agreeing well with wbat is known about tbe relations of tbese two 
crustaceans. The »Punktsubstanz« in Branchipus is divided into 
neurommatidia as in Astacus\ tbe retinal fibres pass into it, and 
from it emerge tbe fibres that lead to tbe next ganglion as in 
Astacus. Tbese facts seem to me to sbow that wbat I bave called 
the distal ganglion in Branchipus is witbout doubt bomologous witb 
tbe first optic ganglion in Astacus. 
