PARASITIC COPEPOBS— CALIG IB ^:— WILSON. 



513 



direction for some time and is then reversed. Under its influence 

 the contents of the stomach and intestine are thoroughly mixed and 

 brought in contact with every portion of the digestive surface. As 

 there is no valve between the stomach and intestine, the contents of 

 the two can pass back and forth without hindrance. 



The alimentary canal is lined with endoderm, which is continuous 

 with the ectoderm at the mouth and anus. While the general structure 

 of this endoderm is distinct from that of the ectoderm, there does not 

 seem to be very much difl^'erentiation in tlie difterent body regions. 

 It is almost exactly alike in structure throughout its entire lengtli. 

 But in ])oth the stomach and intestine it is thrown up into longitudiinil 

 folds which increase the digestive 

 surface. 



In both C'digut^ and LejxjoplitJuirus 

 these folds increase in size as tliey 

 pass ])ackward from the anterior end 

 of the stomach and attain their maxi- 

 mum in the genital segment, after 

 which they decrease toward the rectum. 

 Connected with these folds and usu- 

 ally most abundant alongside their 

 crests are numerous gland cells, which, 

 doubtless, secrete a digestive juice, 

 since they stain difi'erentl}^ from the 

 remainder of the endodci-m. 



Connected with this alimentary canal 

 are two pairs of digestive glands, 

 which prol)ably function something- 

 like the salivary glands and the liver 

 in higher animals. The lirst pair is 

 situated in the anterior part of the cara- 

 pace and is made up of three portions. 

 The smallest of these is median, and 



situated just in front of the mouth tube. The other two portions are 

 lai'ger, and are located sometimes close to the lateral margin of the 

 carapace, just 1)ehind the first anteiuia^ {^Lcpeophthcifux jxcfoi'dJi^^^ g', 

 fig. 21), sometimes nmch nearer the median \\\\Q{('<ili(jush<»ilt<>). A 

 duct (d) extends from the anteilor portion of each lateral division 

 across to the side of the median division, and the latter giv^es off at its 

 posterior end, just below the o'sophagus, a thii'd duct, which ])asses 

 backward and (Miters the anterior end of the stomach. 



The second pair of digestive glands (g") is situated at about the 

 cent( r of the thoracic area, on either side of and close to the median 

 line, and about opposite the posterior end of the stomach. 



Fig. 21. — Digestive glands in Lepeoph- 

 THEiRtis. (After A. Scott.) d, uucts: 



g', ANTERIOR glands; g", POSTERIOR 

 glands; i, INTESTINE; S, STOMACH. 



