240 Trof. J. E. Daeidcn on the 



in any cycle alike in size and other chavacters ; however 

 strongly bilateral or otherwise varied may be the course of 

 development, the final result is an approximation towards 

 radial symmetry, such as is characteristic of most sessile 

 organisms where the environmental forces act equally all 

 round. Most rugose corals have an almost perfect cyclic plan 

 in the uppermost part of thecalice, though we know that this 

 is founded upon decidedly bilateral developmental stages; 

 likewise the cyclic disposition of the organs in the adult 

 stages of nearly all actinians and corals gives scarcely any 

 hint of their strongly bilateral developmental sequence. 

 Hence any argument as to the primary or development 

 relationships of the septa founded upon adult appearances 

 Las little or no value. 



Gordon errs with Kuntli and others in assuming that each 

 of the external grooves on the surface of a lugose corallum 

 represents a septum formed in orderly sequence within each 

 quadrant (see Gordon^s fig. 15). As a matter of fact only 

 alternate grooves correspond with principal septa (entosepta), 

 and it is these alone wiiicli have any sequence value. This 

 is manifest from the series of sections represented in Hgs. 1-8. 

 In figs. 1-6 only entosepta are yet present, and correspond 

 with alternate external grooves, while figs. 7 and 8 show 

 that the smaller sejtta (exosepta) arise almost simultaneously 

 at a rather late developmental stage, and are tiius of no 

 significance as regards septal sequence. 



Attention may now be directed to the proof which Gordon 

 has to offer in support of iiis contention that the primary 

 septal jjlan of the rugosids is tetrameral. He fully recognizes 

 the difficulties attendant upon securing sections through the 

 tips of the coralla, and ai)i}arently has not succeeded in 

 obtaining such ; for the only evidence he adduces rests upon 

 a couple of decalcified silicified specimiens of Sirei'telasma 

 prof unduDij one, of which was broken during examination; 

 witii such material study must necessarily be limited to 

 surface views. He states that " of the four primary septa 

 represinied in the drawing [/. c. tig. J 6], the counter septa 

 extended farthest down, the cardinal next, and the alar 

 next/' and claims that these four septa extended larthest 

 down into the base of the caliceand are the only true primary 

 members. 



1 likewise have in my possession about a dozen decalcified 

 specimens of S. prof nudum, of all sizes, which present all the 

 a| pearanccs described by Gordon, and in some the earlier 

 sti.ges are more completely preserved than Gordon's figures 

 and remarks indicate his two exan)ples to be. 1 have already 



