42 THE WORLD OF THE SEA. 
button. The disc, or cellular plate, has radiating compartments ; 
this plate, at first semi-transparent, thickening as it ages. The 
lower confervoid whorls sometimes remain in fragments, or leave 
their traces in rings, so that, when they reach the top, circles of tufts 
are formed, which surround the centre of the head.” Sometimes 
two of these hat-like expansions are found one above the other. 
Marine plants form neither calyx nor corolla; they have no true 
stamens nor yet true pistils; but by a marvellous compensation, 
as we shall find in the following chapters, many marine animals 
ACETABULUM. 
are organised, and very often grouped, like real flowers. Wonderful 
element, where animals flower and vegetables bear no flowers! 
For a long time botanists were totally ignorant of the mode in 
which marine plants were propagated. They were classed among 
the cryptogamic plants, or plants that have no visible seed organs. 
We now know that the alge are reproduced by corpuscles, male 
and female, which are often endowed with wonderful rapidity of 
motion. If marine animals have borrowed from the land vegetation 
the form of their flowers, the marine vegetables in their turn have 
borrowed from the land animals something of their independent 
motion. In 1793 Girod-Chantrans first pointed out, but without 
any attempt at explanation, the kind of spontaneous movement of 
the green granular matter of certain of the alge. He erroneously 
supposed that this matter was an agglomeration of animalcules, 
similar to those found in some polypes. In 1817 Bory de Saint- 
Vincent discovered beyond all doubt, and showed in a most clear 
manner, that the granules possessed a locomotive power. His 
observations were confirmed by Gaillon, of Paris, and Agardh, of 
LL 
