NO. 2104. NORTH AMERICAN PARASITIC COI'EPODS—WILSON. 17 



the body of the sardine, and crosses over in the midst of the muscles 

 to the hiteral portion of the vertebral column, going along one of 

 the faces of the series of spinous hypophyses to a distance of about 

 1 cm" (1905, p. 32G). 



Here the cephalothorax seems to be able to cling to the bony frame- 

 work, as a woodpecker clings to a tree, and in order to do this the 

 cephalothorax must be definitely adjusted to the framework. The 

 crossing over to the hypophysis and the adjusting of the cephalo- 

 thorax again produce torsion. 



In the case of Pennella on the swordfish there is a more marked 

 twisting about before the final adjustment. The distance to be pene- 

 trated through the flesh is always several inches, and it seldom hap- 

 pens that the parasite gets very near to a blood vessel at first. Like 

 the sardine Lernaean it starts perpendicularly to the axis of the 

 fish's body, but often meets some obstruction around which it must 

 turn aside. And when it has reached the body cavity it is compelled 

 to move backward or forward, to the right or to the left before it can 

 find a suitable food supply. 



The result is that the head and neck of the Pennella is often 

 twisted in corkscrew fashion or even thrown into a coil inside of the 

 enormous cyst. The author has tAvo of these cysts, taken from a 

 200-pound swordfish, in one of which the cephalothorax of the para- 

 site describes a complete circle, 1^ inches in diameter, while in the 

 other it takes the form of an ellipse \% by 2^ inches. 



Such a coiling of the cephalothorax and neck must be accompanied 

 by a considerable torsion of the body, and would very easily over- 

 come the external resistance of the water. We are forced, therefore, 

 to the conclusion that the real cause of torsion is internal, inside the 

 tissues of the host, and not external. In the fresh-water genus 

 Lernaea it sometimes happens that the torsion accidentally proceeds 

 much farther than usual. Thus one specimen showed a direct tor- 

 sion of 315°, or seven-eighths of a complete revolution, Avhile another 

 showed four complete revolutions, 1,440°. 



Food. — Whatever ma}' be the case with parasites of other families 

 there can be no doubt that these Lernaeidae feed upon the blood of 

 their host. 



The simple fact that they burrow through the llesh until their 

 head and mouth are brought into close proximity with some large 

 blood vessel, and sometimes penetrate into the heart itself, leaves 

 us no choice but to conclude that the parasite is making sure of a 

 copious food supply. During the first free-swimming period the 

 larvae of both sexes niaj', and probably do, obtain food from the 

 plankton like other copepod larvae. But during the parasitism 

 which follows this free-swimming period it is just as probable that 



77403— Proc.N.M.vol.5»— 17 2 



