304 SEA-SIDE STUDIES. 



Cylindrical aspect. This animal is also seen somewhat 

 different in structure, but most obviously differing from 

 the solitary species in being a long chain of animals. 

 In spite of their differences, they are not two species, 

 but two generations of the same species. The solitary 

 Salpa produces the chain-salpa by " budding ; " and 

 the chain-salpa by " alternation of generations '' (the 

 phrase is Chamisso's) produces the solitary Salpa by ova. 

 Krohn, Huxley, Leuckart, and Vogt (alas ! only one 

 Englishman among four Germans), have since confirmed 

 Chamisso's discovery, which, as Mr Huxley has pointed 

 out, gives him the priority over Steenstrup, not only as 

 to the mere phrase of " alternate generations," but as 

 to the distinct conception of the idea implied in the 

 phrase. Nine years afterwards, in 1828, Milne Ed- 

 wards first announced a similar mode of reproduction 

 among the Ascidians (such as I sketched it just now), 

 without, however, connecting it with Chamisso's dis- 

 covery. In 1835, the Norwegian pastor and indefa- 

 tigable naturalist, Sars, opened that wonderful series of 

 revelations which by himself, Loven, Lister, Dalyell, 

 Steenstrup, Van Beneden, Allman, Forbes, and others, 

 have established the alternation of generations in Po- 

 lypes and Medusse. 



A not less surprising alternation has been discovered 

 in the Entozoa ; but it would occupy too much space 

 to narrate here, requiring much preliminary explanation 

 before it could be intelligible to the general reader.* 

 Let us continue our history. 



* The student will find a complete history of these phenomena in 



