FA RASITIC COPEPODS—CA LIGID.E— WILSON. 



543 



the org'iin.s by nioiin.s of which the larva i:s to ohtaui 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.", 

 tiii'. 43). 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 maxilhe can scarcely be distinguished as minute protuber- 

 ances close to the margin of the car- 

 apace opposite the mouth. The tirst 

 maxillipeds (mxp.') are much shorter 

 and stouter than in the adult, especially 

 ^in the terminal joint. They are tipped 

 with three strong spines or claws ar- 

 ranged in a row, the two inner ones 

 l)eing pectinated like the hind toe of a 

 night-hawk's foot. 



The second maxillipeds, on the con- 

 trar}^ are much longer and more slen- 

 der than in the adult, and again this 

 diti'erence 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 prominentl}^ in a dorsal view. 



The claw, 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 antennie 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 l)ears a pair of rudi- 

 mentary, biramous appendages whose terminal joints are fringed with 

 plumose setse. It was these setge 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, 

 bat difter nuich from their ultimate form. The l)asipods 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-i'.\RTS ok the metasau- 

 PLius OF Caligi'S bonito. m, mouth; 

 mx"., SECOND maxill.e; mxp'., first 

 maxillipeds; mxp"., second maxil- 

 lipeds. 



