648 A Remarkable Life History and its Meaning. (November, 
alternation of generations, as stated by Chamisso, and the history 
of its development, as given in their papers, is as follows :— 
Each egg hatches into a single embryo of the solitary form 
(Figures 48 and 44). After this solitary Salpa has acquired most 
of the adult characteristics, but while it is still very small, part of 
the wall of its body becomes prolonged into a hollow tube, which 
is shown, very much magnified, in Figure 46. The cavity of this 
tube is in free communication with one of the blood-channels 
(1) of the mother, so that the blood can pass into and out of the 
tube and thus supply the material for its growth and develop- 
ment. The tube lengthens very rapidly, and as it grows it bends 
so as to pass round the digestive organs of the mother (Figure 44, 
Fic. 47. Seven animals from a fully developed chain immediately before its dis- 
charge from the body of the solitary Salpa : s, egg ; t, testicle. 
nu) in a spiral (u) which lies between these organs and the outer 
wall of cellulose. Meanwhile a series of constrictions makes its 
appearance upon the surface of the tube (Figure 46), and in à 
short time the spaces marked off by these constrictions assume 
the shape and acquire the organs of young chain-salpx, as shown 
in Figure 44, u. The chain-salpz then are produced by a process 
of budding from the body of the solitary Salpa. 
There are many hundred chain-salpe thus marked off at one 
time upon the surface of the tube, but the forty or fifty nearest 
its free end develop much more rapidly than the rest, though 
uniformly as compared with each other. After their organs are 
perfectly formed, but while they are still very small, they becom? 
