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TEXT-BOOK OF ENTOMOLOGY 



Its inner surface is thrown up into longitudinal folds, generally twelve in 

 number. These folds shine through the outer walls, and are accordingly indi- 

 cated in the drawings of Dufour, Graber, and others. The 

 entire caecum has an external muscular envelope, outside of 

 which are a few isolated longitudinal muscular bands. The 

 folds within are formed mainly by the high cylindrical epithe- 

 lium which lines the whole interior of the cavity. Tracheae 

 ramify throughout all the layers outside the epithelium. 

 There are appearances of glandular follicles in the bottom 

 of the spaces between the folds. (Minot.) 



Burmeister supposed that these caeca were anal- 

 ogous to the pancreas, and this view has been 

 confirmed by Hoppe Seyler, Krukenberg, Plateau, 

 and others, who claim that the digestive properties 

 of the fluid secreted in them agrees with the pan- 

 creatic fluid of vertebrates. 



Fio. 842. Cross-section of mid-intestine of Acilim sulcatm, show- 

 ing the arrangement of the cseca, two tracheae passing into each caecum. 

 After Plateau. 



d. The excretory system (urinary or Malpighian 

 tubes) 



The excretory matters or waste products of the 

 blood tissue of worms are carried out of the body 

 by segmentally arranged tubes called nephrldia. 

 As a rule they arise in the blood sinuses of the body 

 FIO. 341. Larva of and open externally through minute openings in the 



Sciara : x.ffl, salivary , . . , . ,. . 



gland ; ur.t, urinary skin. As there is a pair to each segment (in certain 



tubes ; i, intestine I , i i_ , ,-, 



stomach ; cae, cwcai oligochete worms two or three pairs to a segment), 

 appendages: t. testis. ,1 n. n j j_ i T o.i_ 



they are otten called segmental organs. In the 



annulate worms each segment of the body, even the cephalic or oral 

 segment, originally contains a pair of these excretory organs. These 



