TUNICA TA. 315 



connected Salpa ; so different, indeed, that it might well appear to 

 belong to another type. Chaniisso, Krohn, and Milne-Edwards have 

 ascertained that the Salpa undergoes what is called an alternation of 

 generation, the young creature being unlike its immediate parent. 

 One of these generations is represented by the solitary individuals, 

 the other by the aggregation of individuals. Each solitary Salpa 

 engenders a new form, which is the chained form ; whereas each 

 constituted member of the chain engenders a solitary Salpa. 



Thus a Salpa is not organised like its mother or daughter, but 

 rather like its sister, its grandmother, or granddaughter — another 

 example of alternate generation, which has already been discussed in 

 treating of some of the Hydrozoa. « 



These marine creatures, which pass their lives in a forced com- 

 munity — animals which eat, sleep, or rest always in company — who 

 abandon themselves together to the soft caresses of the waves — these 

 colonies, or rather republics of animals, leading constantly the same 

 monotonous existence — reveal to us very strange things : an identical 

 community of sentiments in a crowd of beings riveted by the same 

 chain, a chain at once physical and intellectual 



