NO. 1783. NORTH AMERICAN LERNJEOPODIDJE—WILSON. 207 



copepodid stage. Kollar's observations on Basanistes Jiuchonis were 

 interrupted, and he was not certain whether there was a brief metanaii- 

 pUus stage after hatching or not. Beneden makes no statement on 

 this point, but he gives us a figure of a metanauplius larva free from 

 enveloping cuticles. Vejdovsky states with reference to Traclieliastes 

 polycolpus that the metanauplius stage is passed wholly inside the 

 egg, the larva hatching in the first copepodid stage. Kellicott, in 

 describing the larva of AcMheres corpulentus, states that he removed 

 some of the brood from the eggs to make sure, and ''found them in the 

 form of the swimming ones," that is, in the first copepodid stage. 

 Claus stands alone in his statement that the larvae of Achtheres 

 percarum, hatch in the metanauplius stage and molt into the first 

 copepodid stage ''after a few hours." 



From a careful examination and comparison of a large number of 

 egg strings of Achtheres amhloplitis during the period of hatching, the 

 present author has come to the following conclusions: 



1. The great majority of the larvae hatch directly into the first 

 copepodid stage, and it is the evident expectation that all should do 

 so. Under natural conditions it is probable that at least 95 per cent 

 hatch in this way. 



2. The actual emergence of the larvae depends on the texture of the 

 external egg sacks. If they soften and crack rapidly the eggs may be 

 let out into the water early enough for the larvae to escape as meta- 

 nauplii. This is more likely to occur if the females have been handled 

 and kept in aquaria than under normal conditions. 



3. The few metanauplii thus obtained are all ready for the molt 

 into the copepodid stage, and this occurs in from ten or fifteen minutes 

 to an hour. Such metanauplii are too stocky, their locomotor organs 

 are too weak, and it is too near the molting time for them to move 

 around much. All they can do is to lie inertly on the bottom of the 

 aquarium until the molt into the copepodid stage. Under natural 

 conditions such premature hatching with its attendant helplessness 

 might easily prove fatal to the larva. 



4. Ordinarily the egg sack does not break open until the movements 

 of the larvae become quite energetic. The transformation into the 

 firet copepodid form is effected inside the egg membranes and the 

 larva comes forth a vigorous and active swimmer. 



In this species therefore the early larval stages up to the molt into 

 the first copepodid stage are so thoroughly fused as to become one 

 single period. There are no definite points of which it can be said, 

 these mark the completion of one stage and the beginning of the next. 

 It is rather one continuous development, and the peculiarities which 

 usually characterize the different stages overlap one another, so that 

 those belonging to several may be present at the same time. The only 

 point of reckoning is the formation of the nauplius cuticle, and even 



