NO. 2063. NORTH AMERICAN PARASITIC C0PEP0D8— WILSON. 587 



every part is in direct communication mth every other part. The 

 blood moves about freely through these open spaces and a sort of 

 circulation is accomplished by a rhythmic contraction of the three 

 pairs of special muscles already described (seep. 584). The muscles 

 in each pan- contract alternately and pull the intestine away from 

 the midhne, now toward the right side and now toward the left, or 

 forwards and backwards. When the intestine is pulled to the right 

 the blood on that side of the body is pushed precipitately forward into 

 the head. At the same time on the left side of the body the blood 

 streams backward from the head to fill up the space formerly occu- 

 pied by the intestine. These motions are reversed when the intestine 

 is pulled to the left, and this backward and forward streaming con- 

 stitutes all the circulation. 



The strong peristaltic movements of the stomach and intestine 

 help to push the blood along if it lies in contact with the wall of the 

 digestive tract. We have used the term blood here, but of course 

 it can bear that name only by courtesy. It is not really blood like 

 that found in the Argulidae, Caligidae, and Chondracanthidae, but is 

 simply the hquid which fills tiie body cavit}". It has no corpuscles 

 but may serve to distribute the oxygen absorbed through the body 

 walls. 



In the male there is not even this apology for a circulation, and in 

 aU those which have been examined there has never been observed 

 a streaming of the liquid contents of the body in any direction. The 

 body of the male is reduced to such a small size that probably enough 

 oxygen can be obtained by direct absorption through the body walls. 



THE DIGESTIVE SYSTEM. 



In the present family tliis consists of a mouth, an esophagus, a 

 stomach, and an intestine. The mouth-tube is turned forward and 

 is the most anterior part of the body, mth the mouth-opening at 

 its tip. The structure of the mouth and the mode of filling it vnih 

 blood have already been described (see p. 577). 



There are no glands connected with the mouth and the only use 

 it serves is as a funnel to guide the blood into the esophagus, which 

 is slender and thread-like and almost straight (fig. 122). 



It passes abruptly into the enlarged stomach, a thick sphincter 

 muscle being found at the point of junction. This latter is in the 

 head and about on a level with the bases of the maxillipeds, even in 

 those genera (ClavelU, Clavellisa, etc.) which have very long necks. 

 In such genera most of the stomach, and by far the most important 

 part, is located in the neck. The stomach passes so insensibly into 

 the intestine that it is impossible to distinguish an}' point of separa- 

 tion. Both stomach and intestine possess thick walls made up of 

 an outer serous membrane, a median muscular layer, and an inner 



