316 PERIPATUS, MYRIOPODS, AND INSECTS. 



primitive enteron (or gut), or as a space or spaces in the unsegmented 

 or segmented mesoderm. Now, in Arthropods the apparent body cavity 



FIG. 1 02. Diagrammatic cross section of an Inverte- 

 brate, with a primary body cavity (be) which is shaded. 

 (After ZIEGLER. ) 



ec., Ectoderm; bl., bladder of nephridium (as in Crustaceans); ex.) 

 excretory duct ; gn., genital organ ; ., ventral nerve cord ; g., gut: yC, 

 funnels of nephridia (as in worms). 



of the adult is not a true coelome, it consists of a set of secondarily 

 derived vascular spaces ; it has been called a pseudoccele or a haemoccele. 



r '/? - s - 



- b ' 



FIG. 103. Diagrammatic cross section of an Inverte- 

 brate, with a secondary and a primary body cavity. (After 

 ZIEGLER.) 



ec., Ectoderm; s.bc., secondary body cavity (as in Lamellibranchs) ; 

 g., gut ; b.c., primary body cavity (shaded); ex., excretory aperture of 

 nephridium ; gn., genital organ ; ., ventral nerve ganglia. 



The true coelome of Arthropods is very much restricted in the adult, all 

 the more so that most Arthropods (e.g., Insects) have no distinct 

 nephridia. 



