322 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 39. 



evidence that there is no anal opening at this stage of development, 

 and also that the walls of the intestine are stronger than the body 

 walls. 



First metanawplius larva. — Three molts occur in from eighteen to 

 twenty-four hours, and the larva then emerges in the first metanau- 

 plius stage (fig. 34). The body form as well as the appendages have 

 changed considerably, but there is yet much resemblance to the 

 original nauplius. 



The body is now an elongated oval, twice as long as wide, and 

 decidedly narrowed posteriorly. The division into regions is indi- 

 cated by notches in the lateral margins and by faint grooves running 

 across the body. The cephalothorax is much the largest division 

 and constitutes fully two-thirds of the entire body. It is elliptical 



o.lmm. 



an. 



Fig. 34.— First metanauplius laeva of Ergasilus centraechidarum. The first maxill.e in 

 this figure are concealed beneath the m.andibles. lettering as in fig. 4, p. 273. 



in shape, as wide posteriorly as anteriorly, with the lateral margins 

 often reentrant. 



The eyes are situated far forward and in contact on the mid-line; 

 they are concealed in dorsal view by the heavily pigmented supra- 

 esophageal gangHon, but can be seen fairly well from the ventral 

 side in most larvse. 



The segments of the free thorax are indistinguishably fused and 

 strongly tapered. The segments of the abdomen are also fused, and 

 tliis region consists of Httle more than a pair of relatively enormous 

 anal laminss, each of wliich is armed with three or four stout setae. 

 The appendages remain very similar to those of the nauplius stage. 

 The first antennae have now become four-jointed, of wliich the ter- 



