ECONOMIC RELATIONS, ANATOMY, AND LIFE HISTORY OF GENUS LERN^A. 1 69 



of attachment. She first burrows through the skin of the host and into the underlying 

 tissues by means of her second antennse, her powerful maxillae, and her maxillipeds, 

 imtil the anterior half of the body is entirely buried. The segments of the thorax then 

 begin their final lengthening and transformation, and at the same time processes or 

 horns, two, three, or four in number, grow out laterally from the cephalothorax into 

 the surrounding tissue and anchor the head securely in place. Once formed, the function 

 of prehension is entirely assumed by these horns for the remainder of the creature's life. 

 The only subsequent use for the second antennse and maxillipeds is to pull the mouth 

 into contact with the food; for this purpose they retain to the full their form and powerful 

 musculature. 



Specimens of variabilis have been found which did not burrow through the skin, 

 but were fastened to one of the fish's scales. In such instances the horns are still devel- 

 oped, but instead of penetrating the tissues they are flattened out upon the scale and 

 more or less fused with it. Here also, therefore, the horns assume the function of 

 attachment to the host, but there is more work left for the second antennse and maxil- 

 lipeds in the procuring of food. 



As a result of the burrowing usually practiced by the larva we find that the tissues 

 of the host are profoundly modified; those in immediate contact with the head and 

 neck of the parasite harden into a tough, leathery skin which helps to hold the creature 

 in place, and which is usually found enveloping the head and anterior end of the parasite 

 after it is removed from its host. There is often also a swelling of the surrounding 

 tissues, so that a good-sized lump or tumor is formed, perforated through the center 

 and with the posterior part of the parasite projecting from the perforation. Sometimes 

 the head and neck of the paraate work about so much within the burrow that it keeps 

 the flesh of the host raw and bleeding, similar to the sores on the sunfish (Mola mola) 

 occasioned by various species of the Caligidae. Le Sueur and Kellicott mentioned such 

 sores in connection with the species obtained by them. 



Location. — ^The larvae are always found upon the gills, either clinging to the fila- 

 ments or to the skin covering the arches. After mating when the female copepodid 

 larva seeks out her final host she fastens to the outside of the body instead of the gills, 

 in the place where she is to be transformed into an adult. Mating and the attachment 

 of the spermatophores has entirely changed her choice of a location and she now seems 

 to prefer the vicinity of one of the fins, usually the dorsal. 



And when six or eight specimens are found upon the same fish they are arranged 

 in a row alongside this same dorsal fin. But they never burrow through the flesh into 

 the body cavity, and hence do not, like some of the other Lernaeidae, attack the heart, 

 the liver, or any other vital organ. 



Relation to mussel glochidia. — It has been found by the author that there is a well- 

 defined antagonism between mussel glochidia and parasitic copepods belonging to the 

 Ergasilidae." 



The same antagonism evidently exists between the glochidia and the copepodid larvae 

 of the present genus. 



During the summer about 150 short-nosed gars {Lepisosteus plaiostomus) were 

 examined for these larvae. These fish were obtained in "Patterson Lake," "Drury 

 Lake," and similar slews, which the fishing crew visited regularly and the fish of 

 which they infected artificially with mussel glochidia. Gars were often obtained in the 



o Bulletin, United States Bureau of Fisheries, vol 34, 1914, p. 345. 



