Alternation of Generations 53 



contents rather than the wall, was of fundamental im- 

 portance, and was the unit of structure of the whole 

 world of life. On the other hand, he declared that it 

 could not be looked at as the unit of function : he denied 

 that the powers and properties of a living body were 

 simply the sum of the powers and properties of the 

 single cells. In this opinion he was not followed by 

 physiologists until quite recently. For many years 

 physiologists held that cells were units of function just 

 as much as they are units of structure ; but in the last 

 ten years there has been a strong return to the opinion 

 of Huxley. 



In 1 85 1 two v^ery important memoirs were published 

 in the Transactions of the Royal Society, which contained 

 the results of Huxley's observations of the interesting 

 animals known as " tunicates." The first of these 

 papers begins as follows : 



"The Salpie, tliose strano^e gelatinous animals, through 

 masses of which the voyager iu the great ocean sometimes sails 

 day after day, have been the subject of a great controversy since 

 the time of the publication of the celebrated work of Chaniisso, 

 De Ani}iialibiis Quibusdam e Classe Vermium Linnceana. In 

 this work there were set forth, for the first time, the singular 

 phenomena presented by the reproductive processes of these 

 animals, — phenomena so strange, and so utterly unlike any- 

 thing then known to occur in the whole province of zoology, 

 that Chamisso's admirably clear and truthful account was re- 

 ceived with almost as much distrust as if he had announced the 

 existence of a veritable Peter Schlemihl." 



According to Chamisso, salps appeared in two forms : 

 solitary forms, and forms in which a number of salps 

 are united into a long chain. Each salp of the aggre- 

 gate form contains within it an embr3'0 receiving nu- 

 trition from the mother bv a connection similar to the 



