1344 



CRUSTACEA. 



correspond to the palpitations in the body.* We have not, however, 

 observed the blood to flow into their setse, and the currents passing 

 into the legs are among the least regular. We are disposed to believe 

 that these pinnulas are not the special organs for this function, but 

 that aeration takes place over the whole surface of the body. It is 

 stated by Straus, that on separating the branchiaB of a lobster, the 

 body absorbed nearly one-half the oxygen usual before the removal of 

 these organs. The thin envelope of the Caligus, and the extent of its 

 external surface, must render its body a far more perfect substitute 

 for branchige than the solid covering of the lobster. The vibrating 

 action of the natatory legs serves to keep up a constant current of 

 water, and thus affords continually a new portion to undergo the 

 respiratory action of the body. It might be remarked that these legs, 

 on account of their breadth, could not act so as to produce this cur- 

 rent 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 special 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. 



Organs of Reproduction. — On each side of the stomach in Caligus 

 there is a large pyriform organ (fig. q), of a glandular appearance 

 internally, and provided with a distinct duct, which extends through 

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

 nuous, 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, correspond with the sper- 

 matic glands in the male and the ovaries in the female. 



In the male, they are rather larger than the buccal mass (fig. 1 1)> 

 and are situated just anterior to the stomach, in part beneath the base 

 of the prehensile legs and the spine of the preceding pair. Their 

 small posterior extremity is produced into a short ligament, by which 

 it adheres above the stomach ; the anterior portions are so enveloped 

 in their cellular or membranous attachments, that they are separated 



* Tliis action is not so rapid and branchial-like as in the Argulus, but takes place at 

 intervals of about one and a half seconds. 



