36 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.53. 



In the external egg sacks development takes j)l'^ce up to the 

 nauplius stage. The larva hatches as a typical nauplius with tho 

 usual three pairs of appendages and one pair of balancers. It swims 

 about freely in the plankton during the nauplius and metanauplius 

 stages, undergoing several molts. On reaching the first copepodid 

 stage it seeks as a temporary host some fish other than the one 

 which is to serve as the final host of the female, and both sexes cling 

 to the gill filament by means of their second antennae and max- 

 illipeds, and feed on the fish's blood. 



Four copepodid stages are passed here on the gills, the genital 

 segment and abdomen becoming gradually perfected, the reproduc- 

 tive organs being developed, and the swimming legs increasing in 

 number and in the number of segments in the rami. During the 

 fourth copepodid stage both sexes become sexually mature and fer- 

 tilization occurs. After fertilization the female leaves the gills and 

 swims about freely again in the plankton in search of a final or per- 

 manent fish host. She fastens to the skin on the outside of the fish's 

 body by means of her second antennae and maxillipeds, and bur- 

 rows into the underlying tissues with the aid of these organs and 

 the powerful maxillae. Soft horns or processes then develop from 

 the sides of the cephalothorax, the body is greatly elongated and 

 enlarged, the ovaries migrate back into the genital segment, and the 

 mature adult stage is reached, in which she continues until death. 



The male remains upon the gills of the first fish host until death, 

 without further increase in size or other transformation, or he may 

 sometimes leave and swim about freely in the plankton ; but he never 

 attains a length of more than a millimeter and a half, does not seek 

 another host, undergoes no changes corresponding to those of the 

 female, and is never found subsequently in the company of the 

 female. 



Genus LERNAEA Linnaeus. 



Lcrnaea Linnaeus, Fauna Suecica, 174G, p. 367. 

 Lcrnaca Linnaeus, Systeina Naturae, 10th ed., 17oS, p. Go5. 

 Schistunis (part) Oken, Lehrbuch Naturgoschic-hte, ISIG, p. 1S2. 

 Lcrncoccra (part) Blainville, Journ. de IMiysique, vol. 9.j, 1S22, p. 375. 

 Lcrnacoccra (part) Nokdmann, Mikrograpiselie r.eitrage, 1S32. p. 123. 

 Lcrnacoccra Buejieistek, Acta Acad. Caes. Leop. Carol. Nat. Cur., vol. 17, 



1S33, p. 309. 

 Lcrnacoccra (part) Milne Edwaeds, Histoire Naturelle des Crustaces, voL 



3, 1S40, p. 520. 

 Lcrnacoccra, all subsequent authors. 



External generic characters of female. — Head a rounded knob 

 projecting from the anterior margin of the cephalothorax and 

 placed nearly at right angles to the body axis, with a deeply buried, 

 tripartite ej'e near the center of the dorsal surface; one or two pairs 

 of horns, simple or forked, on the lateral margins of the cephalo- 

 thorax; sometimes an unpaired horn on the center of the dorsal 



