THE INVERTEBRATES 139 



have been dredged up from depths of a mile below the sur- 

 face. They range in size from "umbrellas" or disks a few 

 millimeters in diameter to disks of a diameter of two meters 

 (2^ yards). They are all carnivorous, preying on other 

 small ocean animals, which they catch by means of their 

 tentacles, provided with stinging-threads. The tentacles 

 of some of the largest jellyfishes, "reach the astonishing 

 length of 40 meters, or about 130 feet." Many of the jelly- 

 fishes are beautifully colored, although all are nearly trans- 

 parent. Almost all of them are phosphorescent, and when 

 irritated some emit a very strong light. 



The so-called "colonial jellyfishes" are floating or swim- 

 ming colonies of jellyfishes and polyps composed of many 

 individuals closely joined. These individuals are all of 

 one species, but are of different forms or kinds, each kind 

 having a special function to perform in the life of the colony. 

 For example, some individuals catch all the food for the 

 colony; some make the motions; some are especially sen- 

 sitive to the presence of enemies or prey, and some produce 

 all the young. These various individuals act like the 

 separate organs of our own body. The beautiful Portu- 

 guese "man-of-war" is one of these colonial jellyfishes. It 

 appears as a delicate bladder-like float, brilliant blue or 

 orange in color, usually about six inches long, and bearing 

 on its upper surface, which projects above the water, a 

 raised parti-colored crest, and on its under surface a tangle 

 of various appendages, thread-like, with grape-like clusters 

 of little bell- or pear-shaped bodies. Each of these parts 

 is a specially modified individual, produced by budding 

 from an original central polyp. The Portuguese man-of- 

 war is very common in tropical oceans, and sometimes 

 vast numbers swimming together make the surface look 

 like a splendid flower-garden. 



The sea-anemones, corals, and jellyfishes compose the 

 animal branch Coelenterata. 



