No. 2.] ANURIDA MARITIMA. 265 
common peculiarity that the mandibles and maxillae are sunk 
deeply in the head up to the points, as in the case of Anurida. 
He speaks of a fold of the skin that causes this insinking which 
is attached to the labrum, and is undoubtedly similar to the 
fold found in Anurida. Campodea, Japyx, Machilis, and Lep- 
isma all agree in general details, but the last mentioned is 
considered by Hansen a transition form between the Thysanura 
and the Orthoptera. The relations as seen in the anuridan em- 
bryo are as follows: The unpaired labrum forms the upper part, 
the front of the pouch, at the back of which work the two 
pairs of jaws, the mandibles, and the first maxillae, while the 
second pair of maxillae has been modified to form the back of 
this pouch. The lateral folds already described make the sides 
and are developed as shown from the intercalary segment. 
The question naturally arises as to what homology this addi- 
tional pair of mouth-parts can have, arising as it does on a dis- 
tinct segment. Viallanes ('91) and Wheeler ('93) agree in the 
following structure of the orthopteran head and brain: It con- 
sists of a protocerebrum, the most anterior segment, forming 
the mass of the supra-oesophageal ganglion, from which the 
large optic nerves are developed. A deutocerebrum and trito- 
cerebrum follow, which together complete the brain and the 
oesophageal collar. Following this is a series of ganglia cor- 
responding to the mouth-parts, which eventually fuse to form 
the suboesophageal ganglion of the adult. These authors find 
distinct mesoblastic somites in the segments of both the deuto- 
and tritocerebral lobes, and hence conclude their equivalence 
in value to any of the succeeding segments. The antennae of 
insects are enervated from the deutocerebrum, and, as has 
been demonstrated by Viallanes ('91) and St. Remy ('90), the first 
pair of crustacean antennae is also connected with this brain 
lobe, the second pair being enervated by the tritocerebrum. 
Hansen homologizes the mandibles in the two groups, but 
does not decide on the antennal homology. It would seem 
clear from the work already mentioned on the brain that the 
homology of the first antennae of the Crustacea with that of 
insects is practically decided. Arguments drawn from the 
absence or presence of either pair of antennae in the higher 
