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 Ohamisso stated "that a 

 Salpa mother is not like its daughter or its own mother, but 

 resembles its sister, its granddaughter, and its grandmother, f 



Immediately after the publication of Brooks' researches 

 on Salpa spinosa, those of Salensky on Salpa dmnooratica- 

 mucronata (a species said to be closely allied if not identical 

 with ;S'. spiinosa) appeared. According to the Eussian 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 (his 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 ;" tlie testis being 

 immature and the egg fertilizt-d by sperm-cells of other hermaphro- 

 dites, in-and-in breeding thus being prevented. 



f 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 that 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 Salpae in one indi- 

 vidual. The Salpm 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. 



