196 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



In the iourth stage (fig. 61) tlie endopodite is two-jointed, "and is tipped with two 

 nonplumose setae. A few hairs occur at the distal articulation on the 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. 02) 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 setae, 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 maxillae, can now be distinctly seen in 

 at least the basis. 



Second maxilla. — The structure of the second maxilla of the first larva is repre 

 sented by fig. CO, plate 29. It consists of two biramous lobes, the coxa and basis, the 

 respiratory plate or "bailer" and median endopodite. The masticatory setai 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 

 seta3 of the scaphognathite are all plumose and 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 scaphognathite to the branchial cavity. 



First maxillvpeds. — 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 setae 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). The 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 setae, 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 what 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. 



