196 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
In the fourth stage (fig. 61) the endopodite is two-jointed, and is tipped with two 
nonplumose seta;. A few hairs occur at the distal articulation on tlie inner side and 
a larger number at the base on the outer side. The other branches have more of the 
configuration and character of the adult state. 
In the fifth stage (fig. 62) the terminal segment of the endopodite is folded back 
toward the basal joint and bent somewhat as in the adult. The inner margin of the 
proximal segment has scattering set;e, and those on the outer side near the base now 
form a dense bunch, most of which are feathered. The tegumental glands, which later 
are so abundant in the foliaceous parts of the maxillm, can now be distinctly seen in 
at least the basis. 
Second maxilla . — The structure of the second maxilla of the first larva is repre 
seated by fig. 60, plate 29. It consists of two biramous lobes, the coxa and basis, the 
respiratory plate or “bailer” and median endopodite. The masticatory seta; are some- 
times jointed and but sparsely plumose. The long sensory seta of the endopodite is 
also marked by transverse constrictions and has a few lateral hairs, while the fringing 
seta; of the scapliognathite are all plumose aud of nearly equal length. The posterior 
lobe is the wider and somewhat spatula-shaped, and this difference is emphasized after 
the second molt. Minor changes which occur in the course of the three following molts 
concern chiefly the endopodite and the conformation of the mouth parts to the mandi- 
bles and of the scapliognathite to the branchial cavity. 
First maxillipeds . — In the first larva these appendages have the form shown in fig. 
58, and if this is compared with the condition met with in the fourth stage (fig. 59) we 
find that the principal changes concern the two-jointed endopodite and the flagelliform 
exopodite. In the fourth larva the latter is bordered on both inner and outer margins 
with plumose hairs. The seta; on both protopodite and endopodite are more numerous, 
and in the latter branch are much reduced. The respiratory epipodite is relatively a 
little larger. 
Second maxillipeds . — In passing through the first four molts the second pair of 
maxillipeds undergo but minor changes (figs. 63, 64, plate 30). Tbe exopodite becomes 
segmented, flagelliform, and setigerous. The segments of the endopodite, particularly 
their inner margins, become more densely studded with setae, many of which are 
serrated. A rudimentary podobranchia is developed. The natural position of the 
appendages in the first three larval stages is shown in plates 20-22. 
Third maxillipeds . — In the early larval stages (plates 20-22) these appendages are 
usually directed forward and bent into nearly a right angle at the third articulation 
from the extremity. In the first larva (tig. 69) the distal ends of the three terminal 
segments (dactyl, propodus, meros) are armed with stout setm, some of which are 
serrated, while the inner margins only of the proximal divisions are setigerous. The 
exopodite reaches beyond the middle of the fifth segment, and is an important swim- 
ming organ during the first three larval stages. 
The right third maxilliped of the fourth larva is shown in its natural form and 
position in fig. 65. The appendage is still partially bent upon itself, as in the first 
larva, but the proximal half (first to fourth segments) has been twisted through an 
angle of 90°, until wliat were the inner and outer margins have come to lie in a 
vertical plane. The proximal joints are trihedral, and what now forms the inner, 
upper margin has developed a row of stout, rather sharp teeth, which are very 
prominent in the adult. The podobranchia, which is rudimentary in the first stage, 
is now well developed. 
