NO. 2194. NORTH AMERICAN PARASITIC COPEPODS— WILSON. 21 



naeenicus, and Lernaea; and in Peroderma it is conical. Further- 

 more, in this latter genus the head and neck are attached at right 

 angles to the trunk, \Yhile in other genera the head alone stands at 

 an angle with the neck. 



In Pennella the anterior surface and often the entire oephalothorax 

 is covered with small globular or irregular processes which help to 

 anchor the parasite firmly in position. In Peroderma and Car- 

 diodectes branched processes are developed from the front of the 

 head alone, while in Phrixocephalus these anterior processes take the 

 form of small lobed and chitinous horns. 



Again in most of the genera processes, flattened dorso-ventrally, 

 are sent out from the lateral and sometimes from the dorsal margins 

 of the head and anterior thorax segment. These afterwards develop 

 into horns, which complete the anchorage of the parasite to its host. 

 There are no horns on Peniculus, Ilaemohaphes, Cardiodectes, or 

 Peroderma, the anchorage being accomplished by the strong claws 

 on the second antennae, by the frontal processes, or by a flexure of 

 the neck. 



In Lernaeocera and Lernaeolophus the horns are well developed 

 and often branched dichotomously ; in the other genera they are 

 nearly always simple. 



Tliese horns are outgrowths of the epidermal tissues and at first 

 are short and wide and soft in texture; subsequently they elongate, 

 become more or less cylindrical, and are gradually hardened into 

 chitin. 



Too much systematic value must not be given either to the number 

 or the arrangement of the horns in any genus or species, although a 

 certain number and arrangement may be typical in each species: loi- 

 example, the five radiating horns in Lemaeenicus radiatus. But 

 there is always so much variation that no dependence can be placed 

 upon negative CYidence; positive evidence is more conclusive. No 

 specimen of any other species has thus far been found which possesses 

 five horns radiately arranged, but there are many specimens of 

 Lemaeenicus radiatus which do not show them. The number and 

 arrangement of the horns depend more upon the difficidties encoun- 

 tered by the parasite in attaching itself to its host, and upon the 

 kind of configuration of the tissue of the host surrounding the point 

 of attachment, than upon any specific inheritance in the parasite 

 itself. "When the head of L. radiatus is buried in Ihe muscles of the 

 menhaden there is no trouble in developing five radiating horns, but 

 the result is very different when the head is wedged between two of 

 the bony plates of the operculum. The horns, therefore, must be 

 given an insignificant place in the determination <»f the species, and 

 it would be extremely rash to establish a new genus simply upon the 

 possession of two extra horns, as Fowler has done. 



