NO. 1783. NORTH AMERICAN LERN^OPODID^— WILSON. 203 



their base (fig. 17) a well-developed claw inside of the skin. The 

 upper lip is elliptical in shape, wider than long, and evenly rounded, 

 with a small protuberance on either side near the posterior edge. 



Just behind the upper lip and a little outside of it lies on either 

 side a short, wide, and bluntly rounded protuberance, one of the 

 paragnaths, which eventually unites with its fellow on the opposite 

 side to form the lower lip. Between the base of the upper lip and the 

 paragnath projects the mandible (md), which is short, uniramose, 

 and tipped with a single seta. 



The first maxilla (m.x\) is biramose at the tip, the outer ramus 

 much shorter than the inner and each armed with short spines. 



The second maxillae {mx" .) are stout uniramose appendages, longer 

 and larger than either pair of antennse, indistinctly three-jointed and 

 terminated by a weak and slender claw. 



The basal joint lies outside of the first maxilla and this appendage 

 does not properly appear in the section shown in fig, 18. It has 

 been introduced, however, from the second preceding section in its 

 proper place with reference to the other appendages. The maxilli- 

 peds (mxp.) lie inside of and distinctly posterior to the second maxillse; 

 they also are uniramose and indistinctly three-jointed, and terminate 

 in a stout claw with a small protuberance at its base. The two pairs 

 of swimming legs are very rudimentary, each leg consisting of a basal 

 joint and two one-jointed rami, armed with long plumose setse. The 

 anal laminae are as large as the rami of the legs, and are also armed 

 with long plumose setae. 



Internal structure of the Metanauplius. — On examining the section 

 shown in fig. 18 it can be seen that there has been considerable 

 internal development. The fine-grained protoplasmic masses at the 

 anterior and posterior ends of the body have increased greatly in 

 size, and the muscles which are to move the appendages are fairly 

 well differentiated. 



This is especially true of the powerful muscles which are to operate 

 the swimming legs and which appear on the dorsal side of the body 

 near the posterior end of the cephalothorax (m). 



The mesenteron (ms.) epithelium has also begun to be formed 

 around the ventral surface of the stomach, but is incomplete on the 

 dorsal surface. From this ventrally formed stomach layer a long 

 process extends backward which is to become the intestine, while 

 another shorter one is given off toward the mouth. The space withm 

 the epithehum is still filled with tightly packed yolk globules, inter- 

 spersed with large vacuoles, and contains enough nourishment to 

 supply the larva for some time to come. This being just previous 

 to hatching so that the internal structure is approximately the same 

 as during the following stage, we can readily see from the condition 

 of the digestive tract that the larva will not be able to take any 



