COVERED-EYED MEDUSAE. 



PART III. 



Fig. 115. Rhizostoina. 



other of the tribe. In the naked-eyed medusae diges- 

 tion is performed in the cavity of the proboscis ; 



but in this order the 

 proboscis is divided 

 into four very long 

 branches ending in 

 club - shaped knobs 

 (fig. 115), and nutri- 

 ent tubes extend to 

 their extremities from 

 the great central cavity 

 in the umbrella. Their 

 broadish frilled bor- 

 ders are divided and 

 subdivided along their 

 whole lengths, and the 

 nutrient canals, which 

 follow all their ramifi- 

 cations, end in numerous fringed pores upon their 

 edges and upon the club-shaped ends of the quadrifid 

 proboscis. These numerous pores are mouths ; they 

 absorb minute animalcules, which are digested while 

 passing through the united canals to the great central 

 cavity of the umbrella, which receives the products 

 of digestion. Eight canals radiate from that great 

 cavity and traverse the umbrella ; and the nutrient fluid, 

 mixed with the sea-water, passes from the great cavity 

 through these canals into an elegant network of large 

 capillary tubes spread on the under-surface of the margin 

 of the umbrella, which is always in contact with the 

 water ; and in this beautiful respiratory organ the car- 

 bonic acid gas is exchanged for the oxygen in the water 

 of the sea. The indigestible part of the food is dis- 

 charged through the mouths or pores, whose edges are 

 prolonged into solid tentacles containing thread-cells, 

 with their usual weapons of offence and defence. Besides 



