PENNATULID.E. 63 



in the sea, using its pinnte in exactly the same manner as 

 fishes nse their fins ; others say that the motion is effected 

 by alternate contractions and expansions of the thick part 

 of the central mass, as well as by a combined action of the 

 polypes. 



When placed in a basin of sea-water, as many specimens 

 have been by acute observers, they have never been observed 

 to exercise this supposed power of swimming, but have re- 

 mained quietly lying, polypes upwards or downwards, just 

 in the same position in which they were placed. In this 

 condition however the whole body has become very consi- 

 derably distended with water, increasing to several times its 

 natural dimensions ; and that is the only approach to motion 

 betrayed by the Pennatida when in captivity. Sir G. Dal- 

 yell remarks that the distension that takes place does not 

 reduce its specific gravity sufficiently to produce an equili- 

 brium with the water; "thus the animal cannot swim." 



It seems to me that the appearance of the body is such as 

 to favour the notion of a creeping movement, which could 

 be easily effected by a slight action of the lower edges of the 

 pinnae ; and this is just the motion which would most pro- 

 bably be missed by observers watching for it. in the case 

 of animals confined in a narrow basin. For it is doubtful 



