NO. 1404. PARASITIC COPEPODS—CALIGIDM— WILSON. 487 



easily accessible in the tins than under the scales. These two reasons 

 are sufficient to explain the preference of copepod parasites for such 

 localities. 



It mig'ht be inferred that in those genera which arc destitute of 

 hinules there would be a somewhat stronger development of the claws. 

 Possil)ly they are a little larger and stouter, but the diiference is very 

 slight, and after careful examination it does not seem sufficient to 

 warrant an}- statement. 



This method of prehension by claws renders it more difficult to 

 remove the parasite from its host. (hUgus comes oil' easily, but it 

 takes a decided pull to loosen one of the other genera, and often the 

 posterior part of the body will be torn away from the anterior without 

 w^eakening- the hold, as noted by Scott. 



Long experience has taught that the best way to remove these para- 

 sites intact is to slip one end of a pair of broad-tipped forceps well 

 under the carapace and lift the copepod off ({uickly as one would a 

 limpet. 



Connected with prehension are the various devices to prevent slip- 

 ping backward upon the fish's body. We miss in this group the 

 spines upon the ventral surface of the carapace and the roug-hened 

 plate with its posterior teeth on the basal joint of the second maxilli- 

 peds, which were so common amongst the Argulidte. 



But we find instead a small plate that often bears spines upon the 

 basal joint of the first swimming legs, and a sternal fork. The broad 

 lamina joining the third legs also, when applied closely to the surface, 

 must act as a powerful preventative to slipping. And these creatures 

 need something that is powerful for they are often found upon the 

 ventral surface of such fish as the flounder, halibut, plaice, and skate 

 which frequent the bottom and often bury themselves entirely in the 

 sand or mud. 



The friction at such times must be very great and tax to the utmost 

 both the flattened form and the prehensile powers of the parasites. 



HOSTS. 



In general llie PleuronectidjB and Gadidie are the most frequent 

 hosts of the Caligids, ])ut many widely divergent families and genera 

 are represented in the host list. They may be found anywh(M-e u|)()n 

 the external surface or in the gill cavity of their host, while a few 

 species are commonly found inside the mouth, the most notal)le instance 

 being the new species of Cali.gu.s from the Bonito. On the outer 

 surface they often prefer the fins, especially the pectorals since 

 these furnish good opportunities for attaclunent and food as already 

 explained. And then as the parasite usually seeks the underside of 

 the fin it must also l)e protected in great measure by the latter from 

 the friction of the water or nmd through which the fish is passing. 



