292 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



Two posterior levators run from the posterior dorsal wall of the 

 stomach backward close together on either side of the mid-line, and 

 are inserted in the dorsal wall of the third thorax segment. The 

 movements of the stomach and intestine show clearly that there must 

 be depressor muscles, anterior and posterior, connected with the ven- 

 tral walls, and similar to those found by Hertog in Cyclops. 



But owing to the opacity of the ventral portion of the body it has 

 been impossible to distinguish them in a living Ergasilus, and they can 

 not be positively identified in any of the sections thus far examined. 



The contents of the stomach just after the parasites have eaten 

 consists of a rusty brown granular mass, usually quite opaque and 

 filled, especially in the anterior portion, with small spherical globules. 

 Both the color and the globules diminish toward the posterior end, 

 and by the time the contents have reached the intestine they become 

 clear and transparent. 



The intestine is a cjdindrical tube starting from the ventral surface 

 of the stomach and running backward through the rest of the thorax 

 and the abdomen to the anus. 



It tapei-s rapidly in the second and third thorax segments and also 

 descends toward the ventral body wall. For the rest of the distance 

 it is about uniform in diameter, but the relative size varies greatly 

 with the peristaltic movements. 



Generally there is a noticeable enlargement in the genital segment, 

 due to the presence of food that has not jet been fully digested. 

 Sometimes specimens may be found which have died with the circu- 

 lar muscles of the intestine wall in a state of rigid contraction. In 

 such instances the intestine appears of the same diameter throughout, 

 and looks like a string of flattened beads. 



At or near the posterior end of the second abdominal segment the 

 intestine passes insensibly into the rectum. The latter is a very 

 short and thin walled tube, connected with the walls of the abdomen 

 by stout retractor and protractor muscles. These produce the open- 

 ing and closing of the rectum which is concerned in anal respiration, as 

 has been repeatedly observed in living specimens under the micro- 

 scope, and prove that this form of respiration obtains in the Erga- 

 silidae as well as in the Argulidse, Caligid^, and all the free swimfners. 



There is apparently only one anal valve in the dorsal wall of the 

 rectum near the anterior margin of the second abdomen segment, 

 instead of the two noted by Hertog in Cyclops. 



By means of the levator and depressor muscles already described 

 the stomach and intestine are moved backward and forward in regular 

 rhythm, the anal valve opening and closing in unison. In this way 

 the coelomic fluid is moved forward in the dorsal chamber and back- 

 ward in the ventral chamber, constituting the only circulation 

 perceptible. 



