120 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.53. 



Abdomen half the length of the genital segment, plumes large 

 and profusely branched, usually with tertiary plumules. Egg 

 strings very slender and often several times the length of the body ; 

 one of the specimens in lot No. 42313, which was itself 120 mm. in 

 length outside the fish's body, had egg strings 350 mm. long. 



First antennae slender and three-jointed, close to the bases of the 

 second pair and turned forward, the joints of about the same size 

 and heavily armed with setae. Second antennae two- jointed, joints 

 the same size, the terminal one chelate, a stout and e^trongly curved 

 claw shutting past a large peg on the inner margin of the joint. 

 Between the basal joints is a short, pointed rostrum, with the usual 

 pigment spot at its center, and a tripartite eye is deeply buried in 

 the tissues over the base of the esophagus; there are no visible 

 mouth parts. The basal plates of the swimming legs are slender and 

 elongated-triangular in shape, the intervals between the successive 

 pairs being represented by the numbers 10, 30, 35 respectively. 



The structure of the mouth framework is shown in figures 130-131. 

 The chitin ring around the esophagus is short and wide, concave an- 

 teriorly and bluntly rounded posteriorly, with only four chitin bands 

 projecting into the cavity of the head, one at each anterior corner 

 and one at the center of either side. There is but a single semiellip- 

 tical area on either side covered with thin and soft membrane; each 

 of these areas starts just in front of the lateral chitin band and ex- 

 tends backward nearly to the posterior margin of the head. It is 

 surrounded by a wide chitin band or ridge, the bands on the inner 

 sides of the areas meeting along the median line, except for a short 

 distance posteriorly. The arrangement of the muscles and frontal 

 processes with reference to these areas and bands is similar to that 

 in Pennella antarctica. 



Immature stages. — A young P. -filosa, 18 mm. in length, taken from 

 a swordfish, is shown in figures 135-139. The antennae and swim- 

 ming legs are the same as in the adult, but in contrast to the latter 

 all the mouth parts are present and are very distinct. The proboscis 

 projects considerably from the ventral surface of the head and is evi- 

 dently retractile. Inside of it at its base lie the mandibles, which 

 are made up of a broad lamellate basal joint, tipped with a curved 

 spine without teeth. The stout muscles connecting the basal joint 

 with the inner walls of the head show that these organs take a promi- 

 nent part in the early activities of the parasite, and may even assist 

 in burrowing through the flesh of its host. The first maxillae are 

 tiny projections on the side walls of the proboscis, each tipped with 

 two long setae. The second maxillae are long and stout; each con- 

 sists of a basal joint armed with two strong claw-like spines, one on 

 the ventral surface near the distal end and the other at the end on 

 the lateral margin, and a distal joint armed with two claws, one 



