JELLYFISHES AND HYDROIDS 



33 



Fig. 9. 



MILKY-DISK JELLYFISH, 



Vineyard Sound. 



find feeding polypites, reproductive polypites and tentacles very 



much as in Velella. 



Poi'iyita is rare along our coast, but between Cuba and South 



Carolina it is sometimes so abundant as to fleck the ocean for miles 



with specks of brilliant blue. 

 The Sea-Blidaber, (Cija- 



nea arctica), is the largest 



known jellyfish. In the cold 



waters north of Cape Cod it 



grows to huge proportions, 



and one was found by Dr. 



Alexander Agassi z which 



measured seven and one-half 



feet across the disk and 



whose tentacles were fully 



one hundred and twenty feet 



long. On the Long Island 

 coast, however, it grows to 

 a much smaller size and 

 thrives only in spring and early summer, disappearing about the 

 middle of June. Large as these creatures are, however, when 

 dried in the sun it is found that the animal substance is only 

 y|o part of the whole ; the vast bidk of the creature's body being 

 composed of sea water. 



The disk is amber-colored with a rosin-colored centre marking 

 the stomach-space. There are sixteen notches at regular intervals 

 around the edge of the disk, and eight of these notches are occupied 

 by sense organs which contain granular concretions. 



On the lower surface of the disk one finds the central mouth 

 surrounded by veil-like lips, and eight clusters of tentacles. 



The eggs are caught in the veil-like folds of the lips and set 

 free as little pear-shaped larva which swim rapidly through the 

 water by means of their cilia. Soon, however, each larva settles down 

 upon the bottom and develops into a polyp having a terminal mouth 

 surrounded by tentacles. After feeding and growing for some 

 months the polyp begins to display constrictions at regular inter- 

 vals, and soon it splits up into a series of disks, each one of which is 

 set free and becomes a jellyfish. 



