NO. 1783. NORTH AMERICAN LERNJiJOPODID.l^— WILSON. 215 



constriction, extending entirely around the body and making a sort 

 of waist. This causes the posterior portion, the body proper, to 

 appear very niucli hke the abdomen in the Hymenoptera. The pig- 

 ment, which in the female (fig. 28) is confined to a single spot on the 

 dorsal surface of the carapace at the center, is in the male distributed 

 as a narrow dendritic line along either margin of the carapace in 

 addition to the central spot. 



The second maxillae and maxillipeds are larger and stouter in the 

 male, longer and more slender in the female. Especially is this true 

 of the second maxillae, which now are the attachment organs. In 

 the male they are little if any longer than the maxillipeds, and they 

 do not increase in length as development progresses. On the contrary 

 they remain about the same length and retain their terminal claws, 

 together with all the musculature connected with them. 



In the female, although the second maxillae may not be very much 

 longer than the maxillipeds when they first take over the attachment 

 filament, they rapidly increase in length until they become fully 

 twice or three times as long. At the same time the musculature is 

 withdrawn from connection with the terminal claws, and finally the 

 claws themselves disappear. 



Of course in subsequent development size enters as a distinctive 

 factor and quickly becomes predominant over the differences just 

 mentioned. The male is to be a pigmy when sexually mature, and 

 hence increases in size very slowly, and never gets to be over a milli- 

 meter in length. The female, on the other hand, grows normally 

 and is 4 or 5 millimeters long when fully developed. 



The later the stage of development, therefore, the greater will be 

 the size difference between the two sexes, and a point is soon reached 

 where this factor alone will enable one to recognize the sex. 



There is very little difference in the appendages between the two 

 sexes. The first antennae of the male are stouter and longer than in 

 the female, and have only the terminal tuft of three short setae. The 

 second pair are relatively shorter, so that the tips of the two pairs in 

 the male are on a level. There is a rather larger knob at the base 

 of the terminal claw of the exopod, and the endopod has three tiny 

 spines on its tip. The mandible reaches more closely to the tip of 

 the mouth-tube, but easily slips outside of the tube as in the female. 

 The first maxillae are shorter and stouter, and the two terminal setae 

 are more conspicuously jointed at their base. These maxillee hardly 

 reach beyond the base of the mandible, while in the female they 

 reach its tip (compare figs. 26 and 31). 



DIGESTIVE SYSTEM. 



Interest of course is centered chiefly on the internal anatomy of 

 the two sexes at this period. On examining a median longitudinal 

 section (fig. 32) of the male larva shown in figure 24, and of a slightly 



