S i6 



RADIATES : ACALEPHS. 



group includes the hydroids known as Sertularians and 



Campanularians. 



The Sub-Order of Siphonophorae comprises hydroid 



acalephs which exist as free moving communities, each 



community being made up of individuals of different 



kinds, yet all conspiring to 

 give the appearance of one 

 complicated animal. 



The Genus Physalia is a 

 prominent one. It contains 

 the Portuguese Man-of-War, 

 R arethusa, Til., one: of the 

 most remarkable and best 

 known of this group. It con- 

 sists of a pear-shaped and ele- 

 gantly crested air-sac, floating 

 lightly upon the surface of 

 the water, and giving off from 

 its under surface numerous 

 long and varied appendages. 

 These appendages are the 

 different members of the com- 

 munity, and perform v differ- 

 ent functions, some of them 

 eating for the whole, others 

 producing medusa buds, and 

 others being the locomotive 

 members, the latter having 

 tentacles that stretch out be- 



Portuguese Man-of-War, P^arrtAusa, Til. m ' nd the floating Community 

 Southern coast of the United States. even to ^g length of thirty 



feet. The air-sac is three or four inches long, or more. 

 On the tentacles of both Acalephs and Polyps there are 

 numerous microscopic lasso-cells Cnidae each con- 

 taining a spirally coiled lasso which can be darted forth 

 at will, and which aids in securing prey. 



