238 



Prof. J. E. Duciclcii on the 



Fi-r. 21. 



Figs. 17-21. — Series of sections sbowing four stflges in the septal develop- 

 ment of IhmcaneUa borealis. The earliest stage available in the 

 coralliim figured already shows six pairs of senta, as Eaturally 

 exposed in ii jr. 17 and as seen on grinding smooth in tig. 18; the 

 subsequent .septa are added as in the three previous species, with tlie 

 exception that in the last figure the number of septa within each 

 middle chamber ('(-(/) c.vcccds 1>\ two ihat wiihin llie xciilru-latLi.il 

 chambers («,, f>)' 



