LIFE HISTORY STUDIES OF ANIMALS. 495 



reproduce by fertilized eggs.^ There is thus, to use Ohamisso's own 

 words, "an alternation of generations. * * * It is as if a cater- 

 pillar brought fortli a butterfly, and then the butterfly a caterpillar." 

 Here the phrase "bring forth" is applied to two very diflerent processes, 

 viz, sexual reproduction and budding. Ohamisso's phrase, " alterna- 

 tion of generations," is not exact. Huxley would substitute "alterna 

 tion of generation with gemmation," and if for shortness we use the old 

 term, it must be with this new meaning. Subsequent investigation, 

 besides adding many anatomical details, has confirmed one interesting- 

 particular in Ohamisso's account, viz, that the embryo of Salpa is 

 nourished by a vascular placenta.^ The same voyage yielded also the 

 discovery of AppendiGularia^ a permanent tunicate tadpole, and the first 

 tadpole found in any tunicate. 



Some ten years after the publication of Ohamisso's alternation of 

 generations in Salpa^ a second example was found in a common jelly-fish 

 [Aurelia). Not a few hydrozoa had by this time been named, and 

 shortly characterized. Some were polyps, resembling the Hydra of our 

 ponds, but usually united into permanent colonies; others were medusae, 

 bell-shaped animals which swim free in the upper waters of the sea. 

 It was already suspected that both polyps and medusae had a common 

 structural plan, and more than one naturalist had come very near to 

 knowing that medusae may be the sexual individuals of polyp colonies. 



This was the state of matters when an undergraduate in theology of 

 the University of Ohristiania, named Michael Sars, discovered and 

 described two new polyps, to which he gave the names, now familiar to 

 every zoologist, of Scyphistoma and Strohila. In the following year 

 (1830) Sars settled at Kinn, near Bergen, as parish priest, and betook 

 himself to the lifelong study of the animals of the Norwegian seas. He 

 soon found out that his Scyphistoma was merely an earlier stage of his 

 Strohila. Scyphistoma has a Hydra-like body less than half an inch 

 long and drawn out into a great number of immensely long tentacles. 

 It buds laterally like a Hydra, sending out stolons or runners, which 

 bear new polyps, and separate before long, the polyps becoming inde- 

 pendent animals. In the midst of the tentacles of the scyphistoma is 

 a prominence which bears the mouth. . This grows upward into a tall 

 column, the strobila, which is supported belosv by the scyphistoma. 

 When the strobila is well nourished it divides into transverse slices, 

 which at length detach themselves and swim away.^ These are the 



' Brooks maintains that the solitary Salpa, which is female, produces a chain of 

 males by budding, and lays an egg in each. These eggs are fertilized while the 

 chain is still immature, and develop into females (solitary Salpse). The truth of 

 this account must be determined by specialists. 



^Cuvier had previously noted the fact. 



•''Leuckart (Zeits. f. wiss. Zool., Bd. Ill, p. 181) remarks that elongate animals 

 tend to divide transversely or to bud axially, while broad animals tend to divide 

 longitudinally or to bud laterally. The question has been raised more than once 

 whether the division of the strobila is not really a case of budding. Leuckart shows 

 that budding and fission can not be separated by any definition ; they pass insensibly 

 into one another. (Wagner's Handb. d. Physiol., art. " Zeugung.") 



