1894.] The Classification of the Arthropoda. 125 
These cerebral elements apparently have different values. 
So far as observations go, the protocerebrum is always preoral, 
and in no case is any appendage developed in connection with 
it. Apparently, the region in which it occurs is to be com- 
pared to the preoral lobe of the annelids, while the two gang- 
lia of which it is composed would correspond to the “ Scheitel- 
platte” of German embryologists. The other cerebral ele- 
ments, on the other hand, are primitively behind the stomo- 
dum, and, in some forms at least, an appendage is developed 
in connection with each. Thus the antenne belong to the 
deutocerebral neuromere, while in Anurida Wheeler has 
shown that the tritocerebral neuromere possesses at an early 
stage a pair of small appendages, which here, as in all Hexa- 
pods, is absent from the adult. 
In the Crustacea, not a few observations go to show some- 
what similar conditions. We find there a protocerebrum with- 
out appendages at any stage, followed by a series of ganglia 
which present many claims to belong to the postoral series. 
In a paper on the Embryology of Crangon (’89), I claimed 
that in that form the antennze were primitively postoral,. 
but since the validity of my observations have recently 
been questioned by Weldon (’92) and Herrick (’92),' they must 
be repeated before they can be accepted. Aside, however, from 
these questionable observations, there are many other facts 
which go to show that the antennal neuromeres belong to the 
the postoral rather than to the prestomial series. There is, 
however, less evidence for this position for that pair of ganglia 
which exist in the lobster (see Bumpus (’91), pl. XVII, fig. 1), 
_ between the protocerebral ganglia and the neuromeres of the 
antenne. It is without appendages, and although its fate has 
not been traced, it probably becomes fused in the “ cerebrum ” 
of the adult? This neuromere is, I am inclined to think, also 
to be regarded as belonging to the same series as that of the 
antenne, 
1 For some remarks upon these criticisms, see my paper (’93), p- 235, foot-note. 
? Professor J. P, McMurrich informs me that he has found these deutocerebral gan- 
glia in the various Isopods (Jara, Oniscus, Porcellio, Armadillidium, etc.) which he 
has studied. 
