24 



AMERICAN HYDROIDS. 



oporculuin would )>e apt to yield first at the editor, as the tentacles would there exert the most 

 force, and then it would tend to split along lines radiating from the center toward the teeth. 

 Tims there would he formed an operculura of triangular flaps, corresponding in number to the 

 teeth of the hydrotheea (tigs. 57-65). 



This explanation seems to be reent'orced by the condition of affairs found in the few forms of 

 .s, i'l iiliii'i llu that ha\ e a perfectly plain margin without teeth. In X. fnrnioxa, for instance, where 

 the operculum is stretched like a drumhead across the aperture, and the margin is perfectly even, 

 the operculum may be ruptured in almost any way. sometimes around the edge and sometimes 



66 



OPERCn.A CIF FIU'R. THREE. AND UXE FLAP. 



Fig. .~7. >'< i-tnl'tri 11>\ ,,/(,'), showing four-valved operc'ulum. 



Fig. 5*. N ''/</'!;' llti .'/".'/''. showing fuiir-valvril nprri'Uhlln. 



Fig. 511. Ki-iiii Innlli i Hllii'ln. slinwing (nur-valve'l opiTriilum. 



Fig. GO. Dii'tii'n-1/iiliiiin Jhtlti'Hti/ii, showing four-valvrd opon-ulnm. 



Fig. 61. Scrtu/afflfn tririt^^nhiln, sin >wing oicn'Ului]i uf ihri-t- valvi-^. 



V\x. t','2. >' rtiilni-ill'i tnr<fi'l>i. sliiiwiii^' nyKTciiluin of thriv vnh'us. 



Fig. M. ftii!i/f> l/ii I'lm/itltsK, showing operculuni i f<nir val\ r '-^. 



Fig. 64. N' I'tiit/n-i Hn 'if tii, shr>\viiiL; oiKTciilum of four flaps. 



Fig. 65. Xi i-tiihiriUn i>i>ft/y>iii"<, yhowiliK oinTcilluin of four Haps. 



Fig. 6i}.J>iiiliiiitinj'iilln.r, showing npiTfiiliini of cmr vahv. 



Fi;-;. r.7. II//ili-ii/l/in[ii/iiJ'<i/futti, showing o]>ercnlinn of out- valve. 



Fig. i;v ll,i<t,'<illni:i t ii<i ji:t'r<//:i, rnd of hyflrotlicca liighly magnified to 



fiilp. '(/i. abi-alllilK- Hiiji; '('/. aiicaillim- Hap. 

 Fig. W.Diiiliiifiii riisitnii, showing olR'-valved opuroulum. 



sho\v a nnliinrntar\ r ahcanline 



in jao-ged and irregular tears across its surface. In this case there are no points around the 

 margin to cause greater tension along definite lines, and hence there is no regularity whatever in 

 the formation of the opercular flaps (fig. :!7). 



In all the cases that I haye soon when' there is a distinct reduplication of the mai'gin, the 

 operculum has also been reduplicated, the reduplications of the latter being equal to those of the 

 margin. When we consider the genesis of the operculum and its relation to the margin, it is hard 

 to conceiye of any explanation other than that there is a direct relation between the process of 

 regeneration of the hydranth and the reduplication of the margin and operculum. 



