646 A VACATION TRIP TO BRAZIL. 
the present voyage, I was surprised at seeing not far from 
the ship that the blue color of the sea turned abruptly to a 
bottle-green. We were evidently on the edge of a current, 
whose boundaries were as well defined as if the blue ocean 
water through which it flowed had been solid land. This 
was probably the outer edge of the current flowing north- 
ward along this coast. ’We struck it immediately, and 
soon entered it, when to my delight I found the difference 
in color was owing to an immense number of little jelly- 
like animals'which swarmed there so as to destroy the 
transparency of the water. Just on the edge of the cur- 
rent these were collected together in the most astonishing 
quantities, but in the blue water a foot from the edge I 
did not see a single one, so sharply defined was the line 
marked. This line ran about E.S.E., and extended to 
the horizon on both directions, while the opposite side, if 
there were any, was not'visible. Half the circle of the 
sea was ultra-marine, half bottle-green. As soon as pos- 
sible I had a bucket lowered, and after many trials some 
of the animals were captured ; I found them to be Salpe, 
a low kind of mollusk, with small, gelatinous bodies, 
almost perfectly transparent, and growing in compound 
communities, which swim by taking water into the cavity 
- of the body, and propel themselves by the reaction caused 
by the expulsion of this water, in the same way as the cuttle- 
fishswims. There is a very interesting law which obtains 
among many of the lower animals, ealica the alternation 
of generations, according to which the offspring is unlike 
its parents, but like its ‘grandparents. These salps are 
good examples of this law, for one generation consists of 
-compound communities, and the next of single individ- 
uals. Some of the chains were three or four inches in 
_ length, and the individuals of which they v were composed 
- size of a go : 
