CO. 20G3. NORTH AMERICAN PARASITIC COPEPODS— WILSON. 



579 



third kind were called secondary teeth (Nebenzahne) , and they are 

 found in a continuous row behind the principal teeth. They are 

 much smaller than the latter and diminish rapidly in size from in 

 front backward. The mandibles in the genus Naohranchia (Kurz's 

 Cestopoda), and rarely in the males of other genera, have no interme- 

 diate teeth, and the other two kinds are often so nearly of the same 

 size that it is hard to distinguish them. 



The mandibles are operated as follows: The base being inserted in 

 the fold of skm outside the proboscis holds the appendage rigidly in 

 position, with its toothed tip at the openmg of the proboscis, the two 

 mandibles almost or just touching, and the two rows of teeth facing 

 each other. The proboscis is then thrust against the skin of the 

 host and the mar- ,„., 



^. 



ginal fringe is flat- 

 tened out, laying 



bare the tips of the M/f \ 



mandibles. These 

 are pushed into the 

 skin far enough for 

 the teeth to get a 

 good hold. The 

 mandibles are then 

 drawn back into 

 the proboscis by 

 means of powerful 

 retractor muscles ^^*~ '' 



{rm, fig. 3), which fig. 3.— Mouth-parts of Lernaeopoda galei (Achtheres selachio 



rnn from tlip hnesp ^^" Kurz). md, Mandible; mx, first maxilla; rm, retractor 



lUn irom Uie uase muscle of mandible; upl, upper lip; vrtl, under lip. The mandi- 



of each mandible ble on the right side of the figure has been retracted and 



11 1 1 i twisted through an angle of 90°. 



backward and out- 

 ward and are fastened to the side wall of the head. As the base of the 

 mandible is pulled by this muscle the skin fold in which the mandible 

 is inserted is turned inward like the end of a glove finger. The 

 withdrawal of the mandibles also brings the fold of the host's skin, in 

 which their teeth are caught, up into the mouth opening. Here 

 the skin is further lacerated by a sawlike motion until the blood 

 flows freely. During retraction the mandible is also twisted through 

 an angle of 90° upon its long axis, as was first discovered by Kurz. 

 This brings the teeth around, so that instead of facing each other, as 

 at first, the toothed portions of the mandibles both point in the same 

 direction — ventrally. This flexion, after the mandibles have been 

 thrust into the skin of the host, gives them a better hold and keeps the 

 wound open so that the blood will flow freely. The maxillipeds, and 

 in some species the second antennas, are also inserted in the host's 

 skin and help to hold it up against the mouth tube. 



