170 GENERAL ZOOLOGY 



In this hydroid there is a bladder which bears a colony 

 of hydroids beneath and there are five kinds of individuals. 

 The nematocysts of Physalia are very poisonous; bathers 

 swimming against the trailing submarine batteries experi- 

 ence great pain. 



FIG. 70. The Portuguese man-o'-war. A, general view; B, sectional diagram 

 to show different kinds of individuals in the colony; e, gasterozoid, or feeding 

 individual; /, dactylozoid; g, dactylozoid with tentacle; i, female reproductive 

 individual; n, male reproductive individual. 



CLASS 2. SCYPHOZOA 



In scyphozoans the medusa stage is always much more 

 important than the polyp. The jellyfishes do not have 

 a velum, and many of them are very large; Cyanea capil- 

 lata, which occurs off the New England coast, attaining a 

 diameter of six feet. The polyp of a scyphozoan is al- 

 ways small and inconspicuous. It forms medusae by a 

 peculiar type of budding known as strobilization, i,e., 

 constrictions are formed about the body so that it looks 

 like a pile of saucers; the top " saucer" periodically breaks 

 off and swims away as a young medusa (Fig. 71, D). 



On account of their large size and great abundance in 

 many parts of the ocean, scyphozoans have been much used 

 for experimental work in zoology and physiology. One 



