124 
president’s address. 
during which time they fed voraciously on other animals, and 
gave rise to numerous broods of new Scyphistomas by budding, but 
underwent no other changes. The next step leading to the final 
discovery was the examination of a Jelly-fish ( Ghri/saora isosceles), 
which, after having been kept for a day in a glass vessel, was 
found to have laid a large number of eggs, which appeared as 
a fine dust at the bottom of the vessel. After thirteen days these 
eggs had developed into Hydra tuba. Before this time Dalyell 
had become familiar with the Ephyra, an organism one or two lines 
in diameter, found from February to March, and resembling 
“ a flock of birds in distant flight, as represented by landscape 
painters.” Although occasionally discovered in the open sea, they 
were chiefly observed in vessels containing the Hydra tuba or 
Strobila ; and when removed from these vessels they were 
frequently replaced by others. Further observations showed in 
course of time that the fixed form was the origin of the Ephyra, 
the remarkable transverse division by which the Hydra tuba is 
converted into a Strobila taking place about March. Although 
Dalyell was not more successful than Sars in demonstrating the 
gradual growth of the Ephyra into the adult Medusa, the fact 
that the eggs of the Medusa had been shown to give rise to the 
Scypliistoma left no doubt that the life-history of the larger Jelly- 
fishes includes a fixed stage differing to an extraordinary extent 
from the adult form. 
A more recent instance may next be taken, in further illustration 
of the results which may be derived from accurate observations on 
living animals. The observations of Mr. W. Garstang* on the 
respiratory phenomena of certain Crabs are of great interest, not 
only as throwing light on the mode of life of these animals, but 
also as showing that “small points of difference between species, 
which, as far as our ignorance permits us to judge, seem quite 
unimportant,” f may, with further knowledge, be ascertained to be 
of great importance in the life of the species. 
* “ Contributions to Marine Bionomics,” Journ. Mar. Biol. Ass. vol. iv 
(N.S.), 1895 — 97, pp. 223, 396, 102 ; see also Quart. Journ. Micr. Sci. vol. xl. 
1898, p. 211. 
t Darwin, ‘ Origin of Species,’ cliap. iv. 
