PROBLEM OF THE M0NT1CULIP0R0IDEA I 7 



latter way the apex of branches often retarded building thick- 

 walled and close-tabulated cells, and sometimes the basal expan- 

 sions did likewise ; and it is evident then that a kind of zoarial 

 maturity exists, simulating if not derived from the "peripheral " 

 stage. Further, specimens in which a mature stage has developed 

 at the apex may renew axial growth and cell characters, a sec- 

 ond maturity following, by which it would seem that environ- 

 mental causes have had to do with the time of maturity. 



In a specimen of Eridotrypa mutabilis Ulr. at hand, a fortuitous 

 branch has arisen from the mature region instead of the axial, 

 and consequently a cell can be traced as axial, peripheral, axial, 

 and peripheral again. Injured or broken zoarial parts are com- 

 monly renewed by thin (axial) cell growth, even in the periph- 

 eral region, a stolon-like expansion first overspreading the 

 dead area. In perigene growth also the young cells arising at 

 the margin are at first more prostrate than later, giving rise to a 

 basal stolonal region, and in thin, laminar, or encrusting forms 

 it is very distinct. In these cases the stolonal has been said to 

 be probably the homologue of the axial immature region of 

 dendroid zoaria. The stolonal and immature regions in these 

 may coincide, but it is wrong to assume that they do in other 

 and all cases. The stolonal part need not be considered as 

 coordinate with the developmental peripheral and axial regions. 

 It seems, in fact, unnecessary to attach any genetic significance 

 to the stolonal region further than that it is incidental to perigene 

 growth. 



In a given species one specimen larger than the other may 

 be so either from more vigorous growth, as seen in larger axial 

 or immature region, or from longer continued growth, as seen 

 in thicker peripheral or mature region. 



Cell increase is, as a rule, intermural, i. e., young cells begin as 

 small, round pits in the wall at the angle between three or more 

 older cells. The reproduction or budding of zooids doubtless 

 took place in the cortex above the zoarial skeleton, and only 

 later the young zooid comes to build a cell, which, however, 

 from its initial, has its own wall, ?'. <?., wall-half. The young cell 



