102 



CILIOGRADE HYDROZOA. 



PART in. 



times the length of the animal, can be instantaneously 

 retracted into cavities at the posterior end of the body, 

 while, at the same time, the marginal filaments are as 

 rapidly coiled up in a series of close spirals. The 

 whole of these complex organs are enclosed within the 

 limits of a pin's head. 



The manner in which these little gems swim is beau- 

 tiful; sometimes they rise and descend slowly, like a 

 balloon, and when they glide along the surface of the 

 water in sunshine, the cilia on the eight meridional 



Fig. 116. A, Cydippe pileus ; B, Beroe Forskalia. 



bands exhibit the most brilliant iridescence. The 

 long cirrated tentacles follow all their motions in grace- 

 ful curves, or hang indolently down, and sometimes they 

 are suddenly stretched to their full length, and as sud- 

 denly retracted, and in all their varied convolutions the 

 cirri that fringe them are in constant vibration, and ex- 

 hibit all the tints of the rainbow. Sometimes these 

 creatures whirl round their axis with great rapidity, but, 

 active as they are, no nervous system has yet been dis- 

 covered in them. 



The common Beroe is like an elongated melon, ob- 



