34 68 



CCELENTERA TES 



ing stalk, and is almost always surrounded by several thicker folded processes for 

 the capture of prey. In some cases the folded edges of these ribbon-like arms fuse 

 together, leaving only small sucker-like apertures. Canals run from the sac-like 

 cavity, representing the stomach to the edge of the disc, where they enter a circular 

 canal, often provided with apertures. The similarity between this apparatus of di- 

 gestive canals, and the arrangement obtaining in the Ctenophora is then evident. 



Penphylia (three-fourths natural size). 



The reproductive organs lie either in special sacs round the stomach, or merely in 

 widenings of the canals. The surface of the skin is provided with innumerable 

 microscopically small stinging capsules, and, thus armed, these so-called Disco- 

 medusae float about in the water, their bodies being but little heavier than the water 

 itself. Indeed, the common blue medusa {Aurelia} is slightly lighter than water, 

 whereas most of these jellyfish are somewhat heavier than that element, and sink 

 during the pauses in their contraction. 



. Discomedusse are also found in the deep sea, one form of a delicate violet, with 

 darker tentacles, being the so-called Periphylia mirabilis, figured below, which was 

 dredged from a depth of over six thousand feet during the Challenges expedition off 

 the coast of New Zealand. 



