ALLERNATE GENERATIONS. 943 
be as much surprised at the sight of its off 
spring as the Hen that has accidentally hatched 
a Duck’s egg. At the right moment this film 
is torn open by the convulsive contractions of 
the animal, which, thus freed from its envelope, 
begins at once to expand. By this time the 
little bud has assumed the form of a Medusoid 
or Jelly-Fish disk, with its four tubes radiating 
from the central cavity. The proboscis, so char- 
acteristic of all Jelly-Fishes, hangs from the cen- 
tral opening; and the tentacles, coiled within 
the internal cavity up to this time, now make 
their appearance, and we have a complete little 
Medusa growing upon the Hydroid head. Gradu- 
ally the point by which it is attached to the 
parent-stock narrows and becomes more and 
more contracted, till the animal drops off and 
swims away, 4 free Jelly-Fish. 
The substance of these animals seems to have 
hardly more density or solidity than their native 
element. I remember showing one to a friend 
who had never seen such an animal before, and, 
after watching its graceful motions for a moment 
in the glass bowl where it was swimming, he 
asked, “Is it anything more than organized 
water ?”’ The question was very descriptive ; for 
so little did it seem to differ in substance from 
the water in which it floated that one might 
well fancy that some Jrops had taken upon 
