GENERATIONS OF SALPA. 403 
and the development of all which are embraced within a set 
progresses uniformly ; there are usually three of these sets 
upon the tube of an adult solitary Salpa.* 
Thus the Salpa reproduces parthenogenetically as in some 
Crustacea and insects, and we have here a true case of “ alter- 
nation of generations.” In 1819 Chamisso stated ‘‘that a 
Salpa mother is not like its daughter or its own mother, but 
resembles its sister, its granddaughter, and its grandmother. t 
Immediately after the publication of Brooks’ researches 
on Salpa spinosa, those of Salensky on Salpa democratica- 
mucronata (a species said to be closely allied if not identical 
with S. spinosa) appeared. According to the Russian ob- 
server, as stated by Huxley, who adopts his conclusions, the 
chain-salpa is a hermaphrodite, and the egg while still in 
the ovarian follicle is fertilized, when the oviduct shortening 
and widening forms a single uterine sac, the maternal and 
* The Development of Salpa, by W. K. Brooks. Bulletin of the 
Museum of Comparative Zoology, III., No. 14, Cambridge, 1876. We 
have presented quite fully the author’s account of the mode of devel- 
opment of the young asexual (lis female) Salpa, without, however, 
adopting his interpretation of the sexes of the two kinds of individuals 
of Salpa ; believing his “female” Salpa to be asexual, and his “ male” 
Salpa to be hermaphrodite, with an ovary and testis, as he has not ap- 
parently observed the fact of the introduction of an egg into the body 
of his ‘‘male” Salpa. On the contrary, it appears to be developed 
originally in a true, simple ovary or “ ovarian follicle ;” the testis being 
immature and the egg fertiliz d by sperm-cells of other hermaphro- 
dites, in-and-in breeding thus being prevented. 
+ This view has been endorsed by Steenstrup, Sars, Krohn, and 
others, especially by Leuckart in the following words quoted by 
Brooks: “It is now a settled fact thet the reproductive organs are 
found only in the aggregated individuals of Salpa, while the solitary 
individuals, which are produced from the fertilized’ eggs, have, in 
place of sexual organs, a bud-stolon, and reproduce in the asexual 
manner exclusively, by the formation of buds. Male and female 
organs are, so far as we yet know, united in the Salp# in one indi- 
vidual. The Sulpe are hermaphrodite.” On the other hand, Todaro, 
in an elaborate memoir (1876), considers the Salpa as the synthetic 
type of all the vertebrata, presenting features peculiar to each class, 
even including the mammals. In his opinion it is an allantoidian ver- 
tebrate, developed in a true uterus, the neck of which, after the life of 
the embryo begins, becomes plugged with mucus. 
