1'A RASITIt ' ( 'OPEPODS—( '. I L1C1D. E— WILSON. 



543 



the organs by means of which the larva is to obtain its first hold 

 upon its host. 



Just posterior to their base is the mouth, which possesses the same 

 framework and mouth parts as in the adult, although the mouth parts 

 are not yet fully developed. On either side of the mouth, close to its 

 base, are the second maxillae, which are also very rudimentary (mx.", 

 fig. 4S). There is no basipod; the endopod consists of a single conical 

 spine, longer and more slender than in the adult, while the exopod is 

 made up of two small circular chitin plates close to the base of the 

 spine. 



The first maxillae can scarce^ be distinguished as minute protuber- 

 ances close to the margin of the car- 

 apace opposite the mouth. The first 

 maxillipeds (mxp/) are much shorter 

 and stouter than in the adult, especially 

 in the terminal joint. The}" are tipped 

 with three strong spines or claws ar- 

 ranged in a row, the two inner ones 

 being pectinated like the hind toe of a 

 night-hawk's foot. 



The second maxillipeds, on the con- 

 trary, are much longer and more slen- 

 der than in the adult, and again this 

 difference is most marked in the termi- 

 nal joint and claw (mxp."). They are 

 so much elongated that they project far 

 beyond the edge of the carapace and 

 stand out prominently in a dorsal view. 



The daw. even at this early stage, 

 is furnished with the small accessory 

 spine on its inner margin, which is 

 found in the adult. 



Evidently these appendages are to 

 serve with the second antennae as pre- 

 hensile organs. They are especially serviceable in this elongated state 

 during the chalimus stage, as will be noted later. (See p. 546.) 



Each of the two free segments of the thorax bears a pair of rudi- 

 mentary, biramous appendages whose terminal joints are fringed with 

 plumose seta>. It was these seta3 seen through the skin of the nauplius 

 which gave rise to the long curved lines on the ventral surface at the 

 posterior end of the body just prior to this third stage. The append- 

 ages represent the first and second pairs of swimming legs of the adult, 

 but differ much from their ultimate form. The basipods are very short 

 and stout, wedge-shaped or oblong, and armed with short spines at their 

 distal ends. The first pair are united across the mid line by a wide and 



Fig. 43.— Mouth-parts of the metanao- 

 plius ok Caligus bonito. m, mouth; 

 mx"., second maxilla; mxp'., first 

 maxillipeds; mxp"., second maxil- 

 lipeds. 



