FRONTAL APPENDAGE—PHYLLOPOD CRUSTACEAN 707 
that the smaller subdivisions of the appendage are added as the 
animal becomes larger (table 1). In both the young and old 
specimens it was found that the appendage was slightly flattened 
on the ventral side, which may be due, however to its contact 
with other parts while it is closed up under the head. 
TABLE 1 
Showing the variation in the number of terminal branches and the apparent corre- 
lation of number with size, that is, age of the animal 
ARRANGEMENT OF 
ARRANGEMENT OF BRANCHES ON Cl Sen anita 
5 BODY LENGTH 
NO. OF SPECIMEN IN MM. ey : 
o. de- No. de- e No. de- No. de- 
veloped veloping No. forked veloped veloping 
ame veto. ean 15 2 1 0 2 1 
Dag: Migs Soa ere 20 2 1 1 3 0 
Oe Sa tt Se 21 3 1 2 3 0 
AAAS a cui ee se 24 3 1 2 3 0 
CD AARON RR erate 38 4 1 2 3 0 
1 See figure 1. 
Microscopic structure 
For the study of the minute anatomy of the frontal appendage 
a complete series of cross-sections, beginning with the outer tip 
and continuing well back into the body of the animal were made 
in celloidin. This series was used primarily for the reconstruction 
work. Thin sections of various parts of the head and frontal 
appendage were made in paraffin. These were stained with iron 
hematoxylin or safranin-gentian violet. Thick sections were 
stained with eosin or borax carmine. 
A typical cross-section (fig. 2) of a frontal appendage shows 
the trunk to be composed of several definite areas. <A thin, 
flexible, transparent, chitinous covering surrounds the whole; 
just inside of this is a layer of epithelial cells, which, although 
columnar for the most part, are modified in certain regions. In 
the mid-dorsal and the mid-ventral regions the columnar epithe- 
lium is produced vertically so that it joins the mass on the 
opposite side to form a continuous dissepiment, dividing the 
appendage into right and left halves. These lateral halves are 
JOURNAL OF MORPHQLOGY, VOL. 26, No. 4 
