650 A Remarkable Life History and its Meaning. { November, 
latter continues to set free chains from time to time, as they be- 
come matured. 
The solitary Salpas themselves are produced in quite a differ- 
ent way. At the time the chain is set free each of its compo- 
nent animals contains a single egg (Figure 47, s) as well as a 
testicle (¢), which is at this time immature and is composed of a 
mass of undifferentiated cells, as shown in the figure. 
The eggs, on the contrary, are fully developed and ready for 
impregnation, which soon takes place, and is accomplished ina 
very remarkable manner. The egg (Figure '48) lies in one of 
the blood-channels (1) of the chain-salpa, which we shall here- 
after callthe “ nurse.” It is bathed freely by the blood, but is not 
_ itself free within the channel, being mounted upon a long stalk (3), 
like a cherry upon its stem, and the end of this stem is attached 
to the large chamber (Figure 45, A), which we have already de- 
scribed as filled with sea-water, and which we shall hereafter 
designate as the breathing chamber. 
In Figure 48, ¢ represents the wall of this breathing chamber, 
and h its cavity, which is open externally and is filled with water 
at each contraction of the muscular bands. As Salpa when 
found at all is very abundant, the water always contains plenty 
of full-grown chains, as well as the young and immature egg- 
bearing ones. The testicle in the full-grown chain-salpa is fully 
formed, and this discharges its spermatic fluid into the water, 
which accordingly contains great numbers of fresh and actively 
moving spermatozoa. Some of these are drawn, with the re- 
spired water, into the breathing chambers of the young nurses, 
and these may be seen to congregate at the point where the egg- 
stem is attached, as shown in Figures 48, 49, and 50. Some 
of these may be seen to penetrate the stem, and work their way 
up towards the egg, which is thus fertilized. After a 
7 
and draws the egg down into a “ brood-chamber,” or pouch, which 
cavity is a diverticulum, so that the egg is still bathed and nour- 
ished on all sides by the blood, and increases in size very rapidly 
during segmentation, some of the stages of which process are 
shown in Figures 51, 52, 58, and 54. After the formation of 
gastrula the blood not only bathes the outside of the embryo bu 
also passes into and out of the gastrula mouth (Figure 55, 11). 
A constriction now makes its appearance and divides the e™ 
