714 A. T. EVANS 
from it. As yet no use has been assigned to this inner portion, 
although it probably functions with the other parts of the second 
antenna during copulation. The outer portion of the antenna 
consists of a long, hard, horny, sickle-shaped hook which, when 
not in use, is bent back under the body. The inner portion of 
the appendage is not attached to the distal end of the basal 
portion, but more nearly to the proximal end. That the inner 
portion is not sensory is assumed by Packard (78, p. 351) 
because no nerves had been found in it. In the female, however, 
Lankester (’09, p. 36) has assigned the probable function of a 
sensory organ to the second antenna. The muscular structure 
of the second antenna, which is mentioned by Packard, probably 
marks it as an appendage of some importance. Whether the 
inner branch functions in connection with the other parts of the 
second antenna as a Cclasping appendage or as an organ for 
stroking the female during the process of copulation is a point 
which can hardly be decided without witnessing the animals 
in coitu. 
In Thamnocephalus platyurus the peculiar inner part of the 
second antenna is lacking but in its stead is the single large frontal 
appendage. Although this appendage outwardly shows no sign 
of being double, a cross-section of it, as has been pointed out be- 
fore, shows that it has probably been formed by the union of the 
two separate parts. From the variation found in the second 
antenna of Phyllopods, ranging from the nearly symmetrical 
appendage in Estheria, through the different forms to Chiro- 
cephalus (in which the inner part has migrated to a position near 
the proximal end of the basal segment of the antenna proper), 
it seems quite logical to assume that this development has gone 
still farther in Thamnocephalus and that the inner parts of the 
second antennae have not only separated entirely from the 
antenna proper, but that the two parts have met in the median 
line of the head and there completely fused. This seems all the 
more logical when it is known that the inner branches of the an- 
tennae are wanting. It might be assumed that the inner branches 
of the antennae were vestigial and that their degeneration had 
gone so far as to entirely eliminate them in the adult. Such an 
