Description of a Species of Caligus. 261 



place over the whole surface of the body. It is stated by Straus, 

 that on separating the branchiae of a lobster, the body absorbed 

 nearly one half the oxygen usual before the removal of these or- 

 gans. The thin envelop of the Caligus, and the extent of its 

 externa] surface, must render its body a far more perfect substitute 

 for branchiae than the solid covering of the lobster. The vibra- 

 ting action of the natatory legs serves to keep up a constant cur- 

 rent of water, and thus affords continually a new portion to 

 undergo the respiratory action of the body. It might be re- 

 marked that these legs, on. account of their breadth, could not act 

 so as to produce this current of water, when the whole margin 

 around is attached. Probably the animal is not thus attached 

 except when it is rendered necessary by the swift motion of the 

 fish ; under which circumstances, there is a sufficient current, 

 without the action of these legs. We may presume that the spe- 

 cial object of these marginal cups is to enable the animal to attach 

 itself, and still keep the principal part of its body free, so that 

 these natatory legs, when the fish is motionless, may have space 

 to act, and sustain a continued current. 



V. Organs of Reproduction. 



On each side of the stomach, there is a large pyriform organ, 

 (PL V, fig, 18, ) of a glandular appearance internally, and provi- 

 ded with a distinct duct, which at first we unhesitatingly pro- 

 nounced the liver. Subsequent observation proved that the duct^ 

 which we had supposed to enter the intestine, extends through 

 the whole length of the thorax into the abdomen, where it is con- 

 tinuous, in the male, with organs known to be seminal, and in 

 the female, with the egg-bearing vessels. These organs, thus 

 shown to be connected with the organs of generation, have been 

 since proved to correspond with the spermatic glands in the male 

 and the ovaries in the female. 



In the male, they are rather larger than the buccal mass, (PI. 

 V, fig. 21,) and are situated jiist anterior to the stomach, in part 

 beneath the base of the prehensile legs and the spine of the pre- 

 ceding pair. Their small posterior extremity is produced into a 

 short ligament, by which it adheres above the stomach ; the an- 

 terior portions are so enveloped in their cellular or membranous 

 attachments, that they are separated with great difficulty. In 

 general appearance, it resembles a pyriform membranous sac, 



