8 FREDERICK IV. SARDESON 



intersected by straight or curved partitions . . . ." That inter- 

 pretation appears in form of a definition only ; and not knowing 

 how it could be applied to the initial part of cells, respectively 

 young zooids, which then must be supposed to have required 

 several generations to reach maturity, the other interpreta- 

 tion will be kept for the present, viz., that each cell is one 

 zocecium. 



Variation in such species as this one would consist in the 

 zoarium growing in one part more than another for some cause, 

 being one-sided ; or it is discoid because of perigene growth, i. e., 

 the cell increase is greatest around the margin ; or, again, it is 

 acrogene. The surface upon which it grew affected its growth 

 also. The cells remain nearly uniformly large, the number of 

 young cells seen at the surface varying. The cell walls appear 

 uniformly thin. 



Those characters are seen at the surface or in transverse thin 

 section. Longitudinal section would show the tabulae to vary, 

 being fewest where cell length most rapidly increased, and the 

 slightly differing rates of expansion of the cell initial. The 

 atter character can also be estimated at the surface. Other 

 species near to this one are in various ways more complex. 

 Thus, 



Diplotrypa limitaris Ulr. has nearly the same manner of growth 

 as Monotrypa magna, differing in smaller size of cells and shapes 

 of their apertures at the surface (PL A, Fig. 3). Here the 

 number of immature cells nearly equals that of the mature ones. 

 Longitudinal section shows that the young or initial part of each 

 cell is long, slowly expanding, or even for some length not 

 increasing, then quite quickly becoming full-sized, mature (see 

 Fig. 4). The tabulae are closer in these initial parts, tech- 

 nically called mesopores. The plan of growth thus differs from 

 that of Monotrypa mag?ia in that in the latter new cells appeared 

 only as fast or numerous as they were to develop into mature 

 cells. In Diplotrypa the new cells appear too rapidly, so to speak, 

 and await their turn to expand into full size ; hence the more 



