PROBLEM OF THE MONTICULIPOROIDEA g 



numerous small cells, mesopores, among the full-sized auto- 

 cells at the surface. The calycal or open part of the cell is shal- 

 lower in small cells or mesopores than in the larger ones, and 

 that is true in all Monticuliporoidea. Also the autocells crowd 

 the mesopores so that the former tend to become circular at the 

 expense of the latter. 



Callopora multitabulata Ulr. began like a Mesotrypa, but acro- 

 gene growth obtained (PI, A, Fig. 5), the zoarium being long, 

 cylindrical, branched, arising from a basal discoid expansion. 

 The tips, or apices, are only then like small Mesotrypa. The 

 greatest growth of zoarium and cell increase was at the zoarial 

 ends, and there the cells increase centrally, so that some were 

 being crowded away and turned their apertures to the peripheral 

 surface, i. <?., away from the axis of growth (PI. A, Fig. 6, c) . 

 The grown zoarium is thus composed of two regions, the axial 

 or "immature" region of vertical cell part (Fig. 6, d, a), and 

 the peripheral or "mature" of laterally directed cell (Fig. 6, 

 c, d). In the peripheral region the cells grew slower in length, 

 have thicker walls and more numerous tabulae, and there are 

 more mesopore cells. The apical parts also become finally slow- 

 growing, thick-walled, with many tabulae and many mesopores, 

 and it is evident that the zoarium grew rapidly to nearly full 

 size; then a retarded or "mature" growth followed. Renewed 

 rapid zoarial growth and a second retardation stage often occurs, 

 wherefore the terms immature and mature regions are pre- 

 sumptious terms. Peripheral and axial regions are better, since 

 they leave the degree of maturity to be described. Upon the 

 thick-walled peripheral and apical part there occur at nearly 

 regular intervals elevations called monticules. These are occu- 

 pied by a small group of larger-sized, cells with mesopores or 

 young cells. On the thin-walled or growing apex, and hence in 

 the axial region, these are represented by a group of likewise 

 slightly large-sized cells, with abundant mesopores, resembling 

 less distinct cell groups occurring in Morwtrypa, etc. Nicholson 

 proved monticules to be points of greater cell increase, and while 



