INTERNAL CAVITIES OF PLEUROBRACHIA PILEUS. 



265 



from either of the points in question we find the current strongly 

 outwards towards the equator, in the floor of the funnel, but soon 

 meet the opening into the paragastric canal. The axial wall of 

 this canal carries cilia which strike oralwards, while on its abaxial 

 wall the cilia strike in the aboral direction. The canal is thus 

 bathed mesially by an in-going and laterally by an out-going cur- 

 rent (text-fig. 2, 8). Exactly the same thing holds good for the 

 ciliation and currents within the tentacle-canals (text-fig. 2, 4). 

 On the floor (oral wall) of the perradial, interradial, and adradial 

 canals the ciliation is outwards, i. e., towards the entrances into 

 the meridional canals. 



The adjacent halves of neighbouring sub-sagittal canals are 

 ciliated along the whole length of their axial walls in the oral- 

 ward direction. This holds good also for the adjacent halves 

 of neighbouring sub-transverse canals. The areas of oralward 

 ciliation thus correspond with the distribution described for the 

 female gonads at the sides of the canals. The axial walls of the 

 remaining halves of all the meridional canals (cf. distribution of 

 the male gonads) are ciliated in the aboralward direction. 



Along the roof (aboral wall) of the adradial, interradial, and 

 perradial canals the ciliation is inwards, i. e., towards the main 

 cavity of the funnel. The walls of the aboral extension of the 

 funnel have an aboralward ciliation, while an oralward reflux 

 takes place down the middle of this extension into the main 

 cavity of the funnel. 



Here mixing occurs and currents are caught up anew into the 

 paragastric, tentacle, and other canals. 



The arrangement above described proved constant for a con- 

 siderable number of large and small Pleurobrachia examined. 

 The tissues are transparent enough to allow the examination to 

 be made in undissected specimens with the help of a binocular 

 microscope. Fine carmine grains can be used to supplement the 

 evidence of the particles floating in the gastro vascular fluids. 

 Mixed with sea-water the powdered carmine will occasionally be 

 ingested into the stomockeum by natural peristaltic action, or it 

 may be injected into this cavity with the help of a pipette. 

 After a short interval the carmine is expelled from the mouth, 

 but meantime in successful cases sufficient particles to be visible 

 have found their way into the funnel and the cavities leading 

 therefrom. 



The specimens were obtained last June at the Millport 

 Biological Station, and the work was done partly there and 

 partly at Glasgow University, the cost of obtaining material 

 being met out of a grant from the Carnegie Scottish "Universities 

 Trust. 



