Zoology. 281 
ing from the eggs has a different form, as in the Medusee, &c., from the 
second proceeding from the buds. The rings of these worms, or the 
development takes place. 
Th 
the Nais; Milne Edwards has observed the sa the Myrianida 
Jasciata (Ann. Sci. Nat., March, 1845); Sars has given another exam- 
ple in the Filagrana implexa. As in the prece case, it is only 
after several generations by buds that the sexual generation appear 
he individuals proceeding from buds and fro are here more 
or Jess similar in external form; th é 
in having no sex, After this comparison, the pretended anomalies 
ear, 
But in the com scidia, it does not appear t 
Sars has shown that the. larve gives origin to the compound Ascidi 
Which in mass become fixe can scarcely be doubied that the larva 
here is in the first an exogenous gemmiparism, and in the last ae 
endogenous gemmiparism. doubt we shall soon find other facts o 
the same kind which will show still better the character of these different 
Phenomena. We have thus some generations which resemble their 
immediate parents, and some generations which resemble if Sythe 
Ceding parents. It is this phenomenon which is so striking in the Salpa 
and which has given rise to the term al/ernating generation. 
© may conclude therefore by observing, that these anima 8 ager 
two modes of reproduction, one by eggs and the other by a an 
that the genetic evolutions pass through different phases 1 ; x 
Cases. One of these generations may be called oogenous and the 
i 
tis not then by the term alternation that we express the fundamental 
character of these remarkable reproductions. 
