PROCEEDINGS OF THE UNITED STATES NATIONAL MUSEUM 



isjued H^'5N>vi. Q^Ajl Ay the 



SMITHSONIAN INSTITUTION 



U. S. NATIONAL MUSEUM 



Vol. 84 Washington : 1938 No. 3024 



HYDROCORALS OF THE NORTH PACIFIC OCEAN 



By Walter Kenrick Fisher 



Hopkins Marine Station of Stanford University, Pacific Grove, Calif. 



Hydrocorals comprise those coelenterates of the orders Stylas- 

 terina and Milleporina, which, belonging in the class Hydrozoa, are 

 probably highly speciaUzed offshoots of hydroid ancestors. As in 

 the case of marine hydroids the sexual individuals are entirely different 

 from the feeding polyps. In the Stylasterina, the only order repre- 

 sented in the north Pacific, the gonophore is developed in a cavity of 

 the coenosteum, called the ampulla, which often causes a blisterlike 

 convexity on the surface of the colony, or may be superficially invisible 

 owing to its position below the surface. In all the north Pacific species, 

 represented by adequate material, the ampullae are of two distinct 

 sizes. The smaller have been arbitrarily called male ampullae -v^dthout 

 benefit of microscopic examination ; while the larger, usually twice as 

 broad as the male, have been called female. In some cases the latter 

 are known to house ova or planula larvae. With possibly one excep- 

 tion, the two sorts do not occur on the same colony. In dealing vdth 

 material that is usually desiccated and unfit for histological examina- 

 tion it would perhaps be preferable to employ such terms as major and 

 minor ampullae instead of female and male. That so-called male 

 ampullae are not undeveloped stages of the female is amply demon- 

 strated by their frequently different form and crowded condition. 

 In Allopora polyorchis, a typical case, there would not be sufficient 

 space to allow the small ampullae to expand to the size of the major 

 ampullae, 



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