FRONTAL APPENDAGE——PHYLLOPOD CRUSTACEAN (@ 5) 
assumption would seem to be entirely overshadowed by the pres- 
ence of this singular, double, frontal appendage which may be ac- 
counted for by the explanation of the fusion of the inner branches 
of the second antennae. If the two parts of the second antennae 
in Chirocephalus diaphanus, which are known as the frontal 
appendage, can be conceived as having moved into the mid- 
dorsal surface of the head and there united at their bases, the 
branching of the appendage thus formed would not differ greatly 
from that of Thamnocephalus. Another argument which adds 
weight to the belief that the frontal appendage is of the same 
morphological origin as the inner branch of the second antenna 
of some of the species of Phyllopods is the fact that the muscles 
of the antennae and those of the frontal appendage extend through 
the head for some distance together, appearing almost as a single 
muscle on each side, and finally finding their insertions at the 
same points (fig. 3). The antennal muscles of Streptocephalus 
texanus are attached in the same relative position as those of 
Thamnocephalus platyurus (fig. 8). 
On first sight 1t might seem probable that the queer appendage 
in Thamnocephalus platyurus may have formed by a develop- 
ment of the frontal organ of Claus, which is located in the same 
general region, but that this is not the case may be seen from 
the camera lucida drawing of a sagittal section through the 
parts under consideration (fig. 9), in which it will be seen that the 
frontal organ of Claus is located several millimeters posterior 
to the point of junction of the frontal appendage with the head, 
and that it has the same general structure as the organ of Claus 
in Chirocephalus. 
The function of the peculiar frontal appendage of Thamno- 
cephalus is not known, but, with a knowledge of its morphology, 
some assumptions as to its use may be made. In life the animal 
usually keeps the appendage coiled up closely under the head. 
Now and then, however, it is extended in front of the animal in 
a very conspicuous fashion. There are no muscles for expanding 
the appendage, so that it must be pushed out in some other way, 
probably by the distension and subsequent inflation of the large 
sinuses with blood. Upon filling, the sinuses would expand the 
