150 SEAWEEDS 
branes are strongly calcified and stratified. Acicu- 
laria, which has both corona superior and inferior, is 
distinguished from Acetabularia by the fact that its 
spores are strongly calcified (those of Acetabularia 
are free from incrustation), and adhere in clusters. 
Acicularia contains both living and fossil forms. The 
latter are A. Andrussowt and A. miocenica from the 
Miocene and A. pavantina from the Eocene. 
The Reproductive Organs—The life-history has 
been followed in great detail in A. mediterranea. 
Within the marginal chambers the spores (game- 
tangia) are produced in considerable numbers. They 
rest from one to three months after extrusion, and 
then opening by a lid at one end emit the gam- 
etes. The gametes are biciliated, of equal size and 
same shape, and with a red spot. They conjugate 
usually in pairs, and not only so, but in fours or fives, 
sometimes laterally sometimes in reversed position ; 
but conjugation takes place only between gametes 
derived from different gametangia. After conjuga- 
tion they do not immediately settle down, but 
remain in a state of movement with the cilia in pairs 
still vibrating. The zygote, so formed, eventually 
gives rise to a new cap-bearing generation, after a 
rest of about five months. 
If we apply the theory of alternation of genera- 
tions to the life-history of Acetabularia, we must 
regard the product of the zygote, viz. the cap-bearing 
plant, as the non-sexual one, terminating in the pro- 
duction of spores within its radial chambers. The 
sexual generation is represented by the spores which 
without any vegetative manifestation become them. 
