



B 



Figure 46. Three stages of the development of the sea 

 cucumber Holothuria tubulosa (by Krohn) . 



A and B: a — anus; b — digestive cavity, 

 Id — anus; c, d, e — rudiments of the 

 :estine, stomach and pharynx. 



C: 

 inte 



The alternation of sexual and asexual generations in 

 Salpa was described by Chamisso as follows: 



The species of Salpa is found in double form: each 

 generation of the species is dissimilar to its 

 parents, but through birth posterity is similar to the 

 last, so that any Salpa differs from its parent but 

 is identical with its grandparents. Both forms are 

 similar to headless molluscs, hermaphrodites or the 

 female sex. Both of them are viviparous, but one of 

 them is a solitary animal, the originator of many 

 descendants . The other represents a complicated 

 branch consisting of animals, each united with the 

 others by the necessary connection which gives birth 

 to one descendant. These changed forms of the unchanged 

 species are called solitary (Proles solitaria) and 

 aggregated or colonial (Proles gregata) generations, 

 (p. 2) 



534 



