GYMNOBLASTEA ANTIIOMEDUSAE 



267 



will be found to be different stages of growth of the same 

 species. 



The movements of the Medusae are well described by Allman ^ 

 m his account of Cladonema radiatum : — " It is impossible to 

 grow tired of watching this beautiful medusa ; sometimes while 

 dashing through the water with vigorous diastole and systole, it 

 will all at once attach its grapples to the side of the vessel, and 

 become suddenly arrested in its career, and then after a period of 

 repose, during which its branched tentacles are thrown back over 

 its umbrella and extended into long filaments wliich float, like 



A B 



Fig. 132. — Two stages in the development of the Medusa of Lar sdbellarum ( Willsia 

 stellaia). A, first stage with six canals -without branches ; B, third stage with six 

 canals each with two lateral branches. The developing gonads may be seen on the 

 manubrium in A. (After Browne.) 



some microscopic sea-weed in the water, it will once more free 

 itself from its moorings and start off with renewed energy."' 

 The Medusa of Clavatella, " in its movements and mode of life, 

 presents a marked contrast to the medusiform zooid of other 

 Hydrozoa. The latter is active and mercurial, dancing gaily 

 through the water by means of the vigorous strokes of its 

 crystalline swimming-bell. The former strides leisurely along, 

 or, using the adhesive discs as hands, climbs amongst the 

 branches of the weed. In the latter stage of its existence it 

 becomes stationary, fixing itself by means of its suckers; and 



1 " Gymnoblastic Hydroids," Ray Society, 1871, p. 359. 



