150 SEAWEEDS 



branes are strongly calcified and stratified. Acicu- 

 laria, which has both corona superior and inferior, is 

 distinguished from Acctabularia 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. Andrussowi 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 Acctabularia, 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. 



