NO. 1788. 



NORTH AMERICAN EROASILID^— WILSON. 



325 



Fig. 37.- 



- First antenna of second metanauplius 



LARVA, 



time the yolk cells gradually disappear, so that by the close of this 

 stage there are only a few left. The brain is now connected behind 

 the nauplius eye and a rudiment of the genital organs can be detected 

 in a small mesodermal growth on either side of the alimentary canal. 

 The second matanawplius larva. — Two more molts now take place in 

 from twenty-four to thirty-six hours, and the emerging larva shows 

 a more decided oval shape, the body having increased in length, and 

 its posterior end being somewhat narrowed (fig. 36). The anterior 

 antennae are five-jointed; the 

 terminal joint is about half the 

 entire length and copiously sup- 

 plied with setae of all lengths 

 and sizes (fig. 37). The pos- 

 terior antennge also have one 

 more joint than in the pre- 

 ceding stage and the number 

 of their setae have increased. 

 Otherwise they have not essen- 

 tially changed from their pre- 

 vious condition, and still retain 

 the masticatory claws on their basal joints. In the mandibles (fig. 

 38) the exopod has increased in the number of segments and corre- 

 spondingly in the number of its setae. The endopod has lengthened 

 until it is more than twice as long as wide and carries five setae, but 

 it is still one-jointed. The masticatory blade is widened and is now 



armed with four setae, while 

 the basal joint (protopo- 

 dite) of the appendage 

 shows traces of segmenta- 

 tion. The maxillae remain 

 as in the previous stage, 

 except that they have mi- 

 grated a little toward the 

 median line. The maxilli- 

 peds have moved still far- 

 ther inward until they have 

 met on the midline. They 

 have also degenerated 

 greatly and are now noth- 

 ing more than slender papillte, each tipped with a single spine. Evi- 

 dently this is a female larva and these appendages will disappear at 

 the next molt into the copepodid stage. 



It was impossible to carry the larvae into this latter stage, but since 

 they remain free-swimming during their entire metamorphosis such 



Fig. 38.— Mandible of second metnaupuus larva. The 



EXOPOD IS turned BACK IN ORDER TO SHOW MORE DIS- 

 TINCTLY THE ENDOPOD AND THE MASTICATORY PROCESS. 



