P^LCILOPODA. 149 



have assumed a yellowish and opaque tinge, the eye and parts of the 

 embryo are perceptible. In about ten days more, the shell opens 

 longitudinally, and the tadpole issues from it, being at this period 

 about three-eighths of a line in length. Its general form is similar 

 to that of the adult, but the organs of locomotion present a very 

 essential difference. Miiller has described it in this state by the name 

 of Argulus charon. Four oars or long arms, two situated before the 

 eyes and two behind, each terminated by a pennate and flexible pencil 

 of hairs that have a simultaneous motion, by which the animal is 

 impelled by jerks, project from the anterior extremity of the shell: 

 they do not represent the antennae, for they also are visible. The 

 feet with cups are replaced by two stout feet, flexed into an elbow 

 near the extremity, and terminated by a stong hook, with which it 

 clings to Fishes. The only feet proper to the adult, that are developed 

 and free, are those of the second and third pairs, or the two ambu- 

 latory and the two first natatory feet; the following ones are as yet 

 fixed to the abdomen. The heart, proboscis, and ramifications of 

 the appendages of the stomach are distinct. After the first change 

 of tegument, which is effected by a laceration of its inferior surface, 

 the oars disappear, and all the natatory feet are visible. In three 

 days more the second change ensues, but without producing any 

 important alteration. But after the third, which occurs forty-eight 

 hours subsequently to the second, these same feet are converted into 

 those with cups, still, however, preserving the terminal hook. At 

 the expiration of nine days, there is a new change of skin, and the 

 organs of generation, male and female, are apparent; another change 

 of tegument however is required ere the sexes are fitted for copula- 

 tion, so that the period of their metamorphosis extends to twenty-five 

 days. Still, however, they have attained but the half of their proper 

 size. For that purpose fresh changes of the tegument, which occur 

 every six or seven days, are requisite. Jurine satisfied himself of 

 the fact, that propagation never ensues without the intervention of 

 the male. The females, which he kept separate, perished from a 

 disease which was announced by the appearance of several brown 

 globules, arranged in a semicircle on the posterior portion of the 

 clypeus, and apparently formed in the parenchyma, for they were 

 not dispersed by the change of tegument. 



Jrgulus foliaceus, Jurine, Jun., Ann. Mus. d'Hist. Nat. VII, 

 xxvi; Monoculus foliaceus, L.; Argulus delphinus, Herm. Jun., 

 Mem. Apter., V, 3, VI, ii; Monoculus gyrini, Cuv., Tabl., 

 Elem. de I'Hist. Nat. des Anim., p. 454; Ozolus gasteroslei, 

 Lat., Hist. Nat. des Crust, et des Insect., IV, xxix, 1 7; Des- 

 mar. , Consid., L. ; Louse of the Stickleback, Baker, Micros., II, 

 xxiv. This species, the only one of the genus that is known, 



