34 



AMERICAN HYDROIDS. 



A phenomenon so constant and so widespread as this kind of gonangial ornamentation is 

 generally supposed to have some utility to the animals possessing it, and it is not difficult to find 

 a use for these corrugations on purely mechanical grounds. Gonangia are structures that are 



120 



124 



Fig. ll3. 



Fig. 114. 



Fig. IW 

 Fig. 116. 

 Fig. in. 

 Fig. llS. 

 Fig. 119. 

 Fig. IW. 



.Sertularcllaftltformw. 



Xtrtt//rn;//>l ,f/;/anS. 



Scrtiilarclla allmani. 

 Sertularella meriili'inn 

 Ki-rliilnrclla pinnata. 



Scrtii/iff'1/n lii-insriii. 

 Scrlidaria >'/, n-iun. 

 Abictinaria cod. 



ANNULATKD GONANGIA OF THE SERTULARID.E. 



(All figures drawn to the same scale.) 



Fig. 121. Sertulardla Cfnni>li'.rti. 



Fig. 122. Scrtulardla albida. 



Fig. 123. Scrtttltinlla f/ai/i vnr. mbi/ 



Fig. 12J. fSertularclta conlorta. 



Fig. 12S. Scrtulardla p<ili/;n,i int. 



Fig. 126. Sci-tiltdrfftfi iil)<lichut<nn<t. 



Fig. 126a.Sertulnrella subrlichotoma (without tubular neck). 



Fig. 127. Scrtularella rutfosa. 



(an exceptionally slender specimen). 



primarily for the protection of the sexual persons of the hydroid colonies, and the stronger their 

 walls the more efficient is the protection afforded. Man has long ago found that by corrugating 

 sheets of iron or tin their strength to resist lateral pressure is greatly increased. Doubtless the 

 same thing is true of gonangial walls made of chitin, and this may indicate a possible utility for 



