3S4 Ihiivrrslh/ of (Utlifornia I'li/jlical ions iv Zoolofj]/. [■Vol.4 



generation of thr newly fciniiinK p.irl of Itie cxiiskclelon (icciirK. 

 Skeletons of senile fiieius nuiy be I'eiiioved by exnviiil ion, plate 

 l>y plate, often ;it the time of Heliizoc,r(iny. 'Phis exuviation mdkes 

 p(tssil)le readjustments of .specific gravity and speeific .surface to 

 ehani;ini;' conditions of flotation. 



Autotoniy of the two antapicals, or of all three horns is of 

 widespi'ead oeenrrence anionfi' many .species of ('<'ratiinn. It is 

 nior(> abundant in collections from deeper leveLs than in those 

 from the surface. It is caused by local resolution of the eellulo.se 

 wall and is regnlatoi-y in character, j)reservint;- in the horns after 

 autotomy the pi'oportions characteristic of the species. Auto- 

 tomy a.ssists in the adju.stnient of specific surface and possibly 

 also of specific ^I'avity to ehangiiif^ conditions of flotation, espe- 

 cially as affected by temperature. 



Regeneration of the horns with or without preceding auto- 

 tomy may occur in all three horns. It is also regulatory in 

 character and tends to preserve the norm of the species. 



