K0.2194. NORTH AMERICAN PARASITW COPEPODS— WILSON. 9 



of swoidfisli the chitin horns and portions of tlie cephalothorax of 

 females of the genus Pennclla, Avhich had been dead so long that the 

 remainder of their bodies had decayed and dropped off. The same 

 may be said of Lernaeocera hranchialis, whose chitin horns are often 

 found in the throat of codfish and other Gadidae. By thus burying 

 the cephalothorax in the flesh of the host the mouth of the parasite 

 is brought close to some large blood vessel, from Avhence it can derive 

 nourishment. 



Burrowinff. — The different genera choose different blood vessels 

 and also different points on the outside of the host's body from 

 which to commence their burrowing. These differences will be found 

 stated for each genus under the generic characters. Of course the 

 larger the fish infested by the parasite the greater the distance it 

 must penetrate. In the case of Pennella on a large swordfish this 

 distance sometimes reaches 15 or 20 cm. 



It seems probable that this burrowing through the flesh is what 

 causes the intense irritation mentioned by Aristotle, Pliny, and others 

 in the tunny and swordfish, when the latter leap out of the water and 

 often fall on board of ships. 



The actual method of burrowing has never been witnessed, nor 

 from the nature of the case is it likely to be, but there are certain 

 inferences with reference to it which are inevitable. In the first place 

 we know that it is not accomplished by any special or temporary 

 organs, for no indications of anything of this sort have ever been 

 discovered in the larvae. 



On examining the regular appendages with a view of selecting 

 those best adapted for burrowing, attention is at once drawn toward 

 the second antennae and also the maxillipeds in such species as 

 possess them. 



The antennae are exceptionally large and powerful at the very 

 time Avhen the burroAving begins, and are armed with strong chelae. 

 Moreover they are on the frontal margin of the head at first and are 

 then transferred to the dorsal surface. Inasmuch as this is true of 

 every one of these burrowing genera but is found in no other family 

 of copepods there must be some significance in it. At least it would 

 seem to show that these antennae are used in burrowing. 



The burrowing is preceded and may be accompained by an elonga- 

 tion of the thorax and abdomen of the parasite. In the gill parasite 

 Lernaeocera A. Scott stated that the genital segment elongates to 

 fully 15 times its original length. The increase is probably much 

 greater in Pennella^ Lernaea^ and other body parasites; Brian fig- 

 ured a young female Pennella in which the cephalic horns had not 

 yet begun to develop as being G5 mm. in length. Ordinarily the 

 burrowing must be completed before the horns and processes on the 



