98 



LOWER INVERTEBRATES. 



hydroid are not very great, and altliough at first siglit it might seem as if the two 

 theories involve very different comparisons, tliey are in reality identical. 



Okdee I. — PHYSOPHOR.E. 



One of the most interesting forms of Siphonojihora is the 

 genus Aijahna, the name of which dates back to the days of 

 Eschscholtz, the father of the study of actinology. It is the 

 type of a family known as the Agalmid^, and belongs to a 

 larger group of Phj'soidioras or float-bearing Siphonoi^hora. 

 The genus Agalma when floating in the water, will be found 

 to be made up of two kinds of bodies. The first of these are 

 transparent, crystalline in appearance, and are easily detached 

 from their connections with each other ; the second are more 

 opaque, flexible, and smallei-, while they are more tenacious in 

 their attachments to the animal. All are strung together on a 

 common axis or stem which is very flexible in its character. 



The Affalmu as it floats in the water is of a very fragile 

 nature. So delicate is it in fact that it cannot be raised out of 

 the water in the hand without the api>endages being torn from 

 their connections witli each other. The only way to capture it 

 entire is to place under it, as it moves about in the water, some 

 receptacle which will hold liquid, allowing it to float in 

 with the water. The water contained in the receptacle 

 and the animal can then be raised together out of the 

 sea. Even when the greatest care is shown in its 

 capture it retains its appendages but a short time 

 when kept in confinement, and soon loses them 

 all and shrinks to an insignificant size as 

 ompared with its former proportions. 

 The axis or stem of the Agabmi 

 is a most characteristic structure. 

 It extends from one extremity 

 of tlie animal to the other, 

 find affords an attachment 

 ) all the appendages 

 \\liieh make up the 

 whole. It is very 

 flexible, colored a 

 rosy pink, is hollow 

 throughout, and about 

 the diameter of a knit- 

 ting-needle. At one 

 end, which may be 

 called the upper ex- 

 tremity of tlie axis, 

 mall globular liody whieli is called the air-bladder or 

 little sac filled with gas, and in some related genera 



FlO. a'i. — Agalma elegans ; a, float; b, nectocalices; c, covering scales; il. feeding 

 polyjjs; e, tentacles and tentacular knobs; ./", tasters; r/, sexual bells. 



the Stem is enlarged into 

 float. This float contains 



