MUSEUM OF COMPARATIVE ZOOLOGY. 321 
side of the third segment of the primary (external) flagellum. In full- 
sized individuals the free portion of the tertiary flagellum may have 
as many as thirteen or fourteen segments, and the distance between its 
base and the base of the primary flagellum may contain as many as 
eight segments. 
The second pair of antenne» are about as long as the body. The 
mandibles (Fig. 18) are two-branched. One of the branches is terminated 
by a molar surface (Fig. 19), the other by three incisor teeth in the right 
mandible (Fig. 18), four in the left (Fig. 20). 
The first pair of maxilla (Fig. 21) consist of two lobes (a, b), which 
are fringed with set; on their inner borders, and a palpus (7 2) bilobed 
at its free end, 
The second pair of maxille (Fig. 22) are composed of a bifid inner 
plate (protognath, a) fringed on its internal border with set», a middle 
piece (endognatb, » 2) composed of one segment, and a large ear-shaped 
scaphognathite (exognath, 7 e), whose margin is beset with long and 
delicate hairs. 
The first pair of maxillipeds (Fig. 23) have a very complicated struc- 
ture. The inner, prehensile portion consists of two thin, foliaceous lobes 
(a, b), of which the distal (0) is the larger. The edges of both are pro- 
vided with sete. The other parts of the organ are probably tactile and 
respiratory in their function, and consist of a tongue-shaped middle piece 
(ri); an external, large, oval plate which gives off a long palpiform 
appendage (7e); and two small oval plates (e p, e p”) at the base of the 
larger external plate. The inner margin of tho latter, and the distal 
third of its appendage, are fringed with fine sete. The two smaller ex- 
ternal plates (e p, e p’) are of a soft consistency, and very probably serve 
in a measure to aérate the blood. 
The penultimate segment of the endognath of the second pair of max- 
illipeds (Fig. 24) is produced on the inner side into a large lobe, to the 
distal margin of which the terminal segment is articulated. The two 
segments together thus form a broad oval blade, which is reflected upon 
the inner side of the antecedent segments, and lined with sete on its 
oral border. The exognath (r e) is long and slender. At the base of 
the limb, on the external side, are a small roundish epignath (e p) and 
a small but well-formed gill (67). 
The third pair of maxillipeds (Fig. 16) are composed of the same 
parts as the second maxillipeds, but the inner branch (ri) is pediform 
and twice the length of the external branch (7 e). 
The structure of the following thoracic appendages is so well known 
