NO. 1788. 



NORTH AMERICAN ERGASILIDM— WILSON. 



291 



center near the dorsal surface an impaired lobe, nearly spherical in 

 shape, extends forward and slightly upward (a) . On either side of 

 this and just below it an elliptical lobe extends downward and out- 

 ward diagonally (&). From the ventral surface behind the bases 

 of these paired lobes, another lobe (c), spherical or somewhat pointed, 

 extends diagonally downward and outward on either side at right 

 angles to the long axis of the stomach. These lateral lobes are firmly 

 attached by a broad mesentery to the 

 dorsal wall of the head, and do not 

 move during the protraction and re- 

 traction of the stomach. Hence their 

 shape remains practically unaltered and 

 they can be discerned at all times. 



The anterior end of the unpaired me- 

 dian lobe is attached by a pair of long 

 narrow muscles to the dorsal wall of 

 the head near its frontal margin. By 

 these muscles during protraction the 

 lobe is pulled forward almost to a level 

 with the eye and narrowed accordingly 

 (see fig. 15). The oblique lobes do not 

 appear to be' attached at all, or at the 

 most very loosely, and during protrac- 

 tion they are obliterated, leaving only 

 the median and the two lateral lobes 

 in evidence. But during retraction they 

 show distinctly. 



In addition to these lobes at the an- 

 terior end, the dorsal surface of the 

 stomach is also raised for its entire 

 width in two rounded elevations, of 

 which the anterior is about twice the 

 size of the posterior. 



The esophagus enters the stomach behind the base of the unpaired 

 lobe, and between the bases of the first paired lobes. 



At the posterior margin of the second thorax segment the stomach 

 is differentiated from the intestine by a well-defined constriction. 

 The whole of the median unpaired lobe, the first set of paired lobes, 

 and the bulk of the second set project into the head, but the remainder 

 of the stomach is within the first two thorax segments. 



Two narrow anterior levator muscles run from the upper surface 

 of the stomach forward and upward and are inserted in the dorsal 

 wall of the carapace, just in front of the line of demarcation between 

 the head and first thorax segment. 



Fig. 13.— Ventral surbace of female 

 Ergasiluscentrarchidarum. a, Me- 

 dian LOBE OF stomach; 6, diagonal 

 lobe; c, lateral lobe; d, excretory 

 tubes; i, intestine; r, rectum, s, 



STOMACH. 



