FRONTAL APPENDAGE—-PHYLLOPOD CRUSTACEAN 705 
tained food material. The tail of the female bears a large, cres- 
centic spot on each side of the alimentary canal. These spots, 
which vary from flame scarlet along their posterior margin to 
light orange yellow (Ridgway’s ‘color standards,’ plates 2 and 3) 
anteriorly, cover from one-half to three-fourths of the posterior 
lobe of the tail. Similar spots of a smaller size and a lighter 
eolor occur on the tail of the male. The eighteen specimens 
used in this study varied in length from 15 to 38 mm. 
FRONTAL APPENDAGE 
Macroscopic structure 
The frontal appendage, which is present only in the male, 
projects in the middle line from the front of the head, directly 
between the bases of the second antennae. It is from one-half 
to three-fourths as long as the body proper, and at its base is 
slightly larger in diameter than the basal joint of the second 
antenna. The basal one-third of the frontal appendage consists 
of a single trunk, which then divides into two branches, each of 
which further subdivides into two parts about midway between 
their junction with the main trunk and their tips (fig. 1). These 
secondary branches may or may not be further subdivided, the 
amount of subdivision and the resulting number of tips de- 
pending upon the maturity of the individual. In a male 38 mm. 
long, the outer of the two secondary branches bore four sub- 
branches, of which the two proximal ones were forked; and the 
inner branch, three. Just below the division of each of the two 
large branches a small spur occurs on the inner surface of each 
branch (fig. 1, D). This arrangement of the different branches 
of the frontal appendage gives the whole a somewhat arch-like 
appearance when the appendage is correctly spread, since the 
inner branches leave the main branches at an angle and are 
directed upward and forward. In the water the animal opens 
the appendage suddenly and, when seen from above, it appears 
to be more or less flattened. When not in use or extended, the 
frontal appendage is closely folded under the anterior end of 
the body between the bases of the antennae, the smaller tips 
