136 



Papers from the Department of Marine Biologij. 



The gut is markedly compressed dorso-ventrally. There is no defi- 

 nite division into oesophagus, stomach, and intestine, although its 

 much greater size in the central region indicates the probable location 

 of the stomach. At the anterior end the tube tapers more gradually 

 than at the posterior, where it retains a tendency to curve somewhat 

 toward the ventral surface of the embryo. The gut is lined with a 



a>.e. 



i \^ ; " C *S ^t^^f^^^^^^^\^ 



::: ; fe;;;#r|^^ ; L" , ,' : " ^V^^-"'*^ 

 fe L 3S-2aie<jBS .-.-f'.v .'\a -ift 



FIG. 18. Transverse sec- 

 tion taken somewhat pos- 

 terior to that represented 

 in fig. 17, showing first 

 and fourth tentacles cut 

 through their anterior 

 part, and lobes two and 

 three through their pos- 

 terior, a.e., anterior en- 

 terocrele; g, gut; /(, hydro- 

 coele; P, lumen of lobe 3 

 of hydroccele; m, mesen- 

 tery-like strand of tissue 

 connecting the stomach 

 with the wall of the em- 

 bryo; sp., spine; t l , < 2 . *, 

 t*, tentacles 1, 2, 3, 4. 

 X 233. 



FIG. 19. Transverse sec- 

 tion through posterior 

 part of embryo, a.e., an- 

 terior enteroccele; g, gut; 

 Z 5 , lumen of lobe 5 of hy- 

 droccele; p.e., posterior 

 enteroccele; sp., spine; 

 t', tentacle 5. 



19 



single layer of cylindrical cells with clear cytoplasm and centrally 

 located nuclei. The lumen is entirely closed and there is no indication 

 of communication with the exterior. 



Anterior to the stomach, and bending down over it, lies the undivided 

 anterior enterocoele. It is composed of an exceedingly thin layer of 

 cells which lies flatly pressed against the adjacent tissues, except where 



