I 8 FREDERICK IV. SARDESON 



becomes triangular, quadrangular, etc., in proportion as it grows 

 large enough to neighbor on three or more cells. Young cells 

 have shallower calycals and are generally closer-tabulated, but 

 proportionate to their size, as compared to mature ones. The 

 number of young cells in proportion to large ones affects the 

 cell pattern at the surface. This is especially notable when the 

 simplest case of rapid, direct, continuous expansion of young 

 cells is contrasted with that where " mesopores " are numerous 

 (Plate A, Figs. I and 10). 



Mesopores are said to be present if the young cells when 

 about half-grown in diameter, retard or cease their expansion, 

 but, of course, continuing length growth. If the mesopore 

 stage of cell is short, few mesopores, if long, many mesopores, 

 are present. They may outnumber the autocells so greatly that 

 a small proportion only could become autocells. They may be 

 more numerous in the peripheral, mature, or retarded cell growth 

 region. Again, as in Prasopora simulatrix many mesopores 

 remain such while other newer ones develop to autocells. Yet, 

 apparently any mesopore may finally become autocell. They 

 are, however, something more than retarded young cells, in case 

 like Stellipora {Constellaria) , where the angular mesopores are 

 rather larger instead of smaller than the rounded autocells. 



The more distinct the mesopore development the more sub- 

 ordinate they appear to become. The autocells are angular from 

 contact with each other or young cells, but rounded when 

 crowding mesopores, the latter alone remaining angular. Also 

 the mesopores become shallow, the tabulae developing close to 

 the wall margin forming "closed" mesopores, or they even 

 filled solid with superimposed tabulae; or the tabulae overlap the 

 walls, forming " vesiculose " structure. Autocells arise, displacing 

 several mesopores at once, " ccenenchymal gemmation," in some 

 species with vesiculose or even regular mesopores. 



Monticules, as Nicholson pointed out, are rapid cell increase 

 areas. In simplest cases they appear at the surface as mere 

 small elevations or more or less elevated clusters of slightly 

 larger sized cells, among which young cells are seen except 



