110 SYNOPTIC COLLECTION. 



feeding and reproductive zoons. The latter give rise to 

 medusae buds which may be seen in different stages of 

 development in the living animals until finally they 

 become detached and swim away. 



Physalia, or the Portuguese Man-of-war (No. 146; No. 

 147, P. arethusa Till.; No. 148, model of P. pelagica 

 Linn.), has a beautiful pear-shaped float surmounted by a 

 crest or sail, well seen in No. 147. According to the 

 observations of Huxley on young Physaliae it is probable 

 that the float represents the primary Hydra. At the 

 broader end of the lower side of the float are different 

 kinds of zoons; these perform a different kind of work 

 and are therefore unlike in structure. Prof. Agassiz 

 observed that the largest zoons are on the windward side 

 of the animal and are provided with tentacles which vary 

 in length from 20 to 50 feet. 



The feeding zoons are of two kinds, and besides these 

 there are .medusa buds which do not break away as free 

 medusae but are modified into swimming or propelling 

 bells. 



Agalma rigidum Hkl. (No. 149), is a complex organ- 

 ism. It has a flexible hollow stem which is divided into 

 two parts and which bears all the appendages. At one 

 end the stem enlarges to form the air-bladder or float 

 which is reduced and apparently too small to be function- 

 ally useful. The two parts of the stem are called the 

 nectostem and polypstem. The nectostem carries bodies 

 which resemble medusae but which are without a mouth 

 or stomach. If originally medusae, they have become 

 reduced into propelling organs or swimming bells. The 

 polypstem has covering scales probably for protecting the 

 bodies beneath them. These bodies are of three differ- 

 ent kinds: nutritive zoons, small organs called tasters 

 which, according to Haeckel, 1 have a sensory function 

 acting as organs of taste or sight, and sexual bells or 



iChall. Rep., Zool., XXVIII, part 77, 1888, Siphonophora, p. 16. 



