30 ART. 11— K. YEXDO: 



having a few cortical cells, of course calcified, yet remaining un- 

 detached. 



In tlie unizonal genicula the cells undergo further development 

 in only the slightest degree. The cells of the basal genicula of Amp. 

 abenans, for instance, have their length nearly equal to the upper ones 

 and the thickness of their walls seems to have received no addition. 

 Sdlms-Laubach 1) observed the formation of transverse septa in the 

 genicular cells of Corallina. These transverse septa, were quite 

 common in the genicular cells of the Eurytion ; but, as far as the 

 present writer could examine, there was no septum formation in the 

 cells of unizonal genicula, to which category all of Corallina belong. 



The formation of the multizonal genicula is fundamentally dif- 

 erent from that of the unizonal. The first step is the decalcification 

 of a certain part of the frond, bounding several zones of the periclinal 

 cells. This process seems to be carried on in a comparatively short 

 time. The boundary of the decalcified area is very sharp, and can he 

 easily traced by a staining reaction after the frond has been artificially 

 decalcified. The area seems not to extend further than the limit 

 formed at the first step of the formation. 



While decalcification is taking place, the cortex around it remains 

 unaltered for some period. But afterwards a part of the cortex, mostly 

 on the fiat surface of the frond, comes off in shape more or less corre- 

 sponding to the decalcified area. The result is the " fenestraform " 

 geniculum. 



As the geniculum develops further, the cortex around it con- 

 tinues to break off, until a complete '" bandform " geniculum is visible 

 to the naked eye. 



As soon as the fenestraform has appeared, the genicular cells 

 begin to undergo further modifications. It is the formation of the 



1). Corallina : p. *-" J - 



