252 



CUTTLE-FISH, MOLLUSC A, ETC. 



animal ; but all " are arranged in this stellate form 

 because they have one anus in common, out of which 

 excreta, &c., are ejected." The mouth of each animal 

 may be seen like a dot in the " ray." * This is sur- 



Fig. 1 86. 



Fig. 185. 



Botryllus on frond of 

 sea-weed. 



a, Botryllus poly das', b, Separated indi- 

 vidual, forming a " ray" of one of 

 the star-like objects. 



rounded by cilia, and when alive, is in reality a very 

 active organ, producing miniature whirlpools in the 

 sea water, and thus obtaining fresh oxygen and food. 

 The common anus forms the centre dot of each 



* Throughout this book such circulating currents in various animals 

 are frequently mentioned, and they are now particularly adverted to, 

 because it is by imitating them in the machinery of aquaria that the best 

 biological results are attained. In this way, perhaps unconsciously, we 

 do as Nature does, and then find that she, long previously, has done 

 the same thing in a far neater and better manner. 



