NO. 178S. 



NORTH AMERICAN ERGASILID^— WILSON. 



319 



extrusion into the external sacks is to keep them properly aerated. 

 But this is of vital importance here as in all tlie Crustacea. 



If the eggs are so far advanced that they will hatch out in from 

 twenty-four to thirty-six hours after capture, then Nordmann's 

 statement holds true. And if they are placed in fresh water it makes 

 no difference whether the mother is alive or not — they will hatch just 



Fig. 30.— Newly hatched nauplius of Ergash-us centrarchidarum , dors^u. view. 



the same. But if a longer period is required, it will be found almost 

 impossible to keep the eggs sufficiently aerated, and they then die 

 before hatching. 



The Nauplius larva. — The newly hatched nauplii are extremely 

 minute and swim at once toward the light, being positively helio- 

 tropic. On being viewed under normal conditions they are seen to 

 have the typical nauplius form, elliptical or oval in outline and 

 strongly flattened (fig. 30). Yet they differ very noticeably from the 

 nauplii of the Caligida? and 

 considerably from those of 

 the free-swimming forms, as 

 can be seen in the following 

 description : 



In dorsal view there are 

 often apparently only two 

 pairs of appendages, corresponding to the first and second antenna?, 

 which are of the usual structure and proportionally much larger than 

 in the Caligidse. Each of the first pair is uniramose, two-jointed, and 

 terminates in two unequal seta?, the anterior of which is much longer 

 than the posterior (fig. 31 ) . These first appendages are carried straight 

 forward, side by side, while the second pair extend outward at right 

 angles to the body axis. This latter pair are stouter than the first 



Fig. 31.— First antenna of nauplius of Ergasilus 

 centrarchidarum . 



