236 



CIKRIPEDIA. 



motive organs consisting of a large pair of limbs pro- 

 vided witii a sucker and hooks, adapted for mooring 

 themselves at pleasure to any foreign object ; and 

 also of six pairs of swimming-legs, that act in con- 

 cert like oars. Besides these, they have a tail bent 

 under their body, consisting of two joints, and ter- 

 minated by four bristles, which constitutes an ad- 

 ditional apparatus of propulsion. Thus endowed, 

 thev swim alomr in a series of bounds, the oars and' 



Fig. ISO.— young of baexacle. 



tail giving, in measured time, successive impulses. 

 They have, moreover, large lateral eyes, and the body 

 is covered with a sort of shell, such as we see in the 

 early state of certain Entomostracans ^Cyclops), 

 which they closely resemble. Believing little crea- 

 tures so constructed to be the larvse of some Crusta- 

 ceans, they were kept by Mr. J. Y. Thompson in a 

 glass vessel, covered to such a depth with sea- water, 

 that they could be examined at any time by means of 

 a common magnifying-glass, and, to his great surprise, 

 in the course of a few days they threw off their larva 

 skins, and became firmly adherent to the bottom of 

 the vessel, changed into young Barnacles, such as 

 are usually seen in the spring-time intermixed with 



