228 CONTRIBUTIONS TO THE NATURAL HISTORY 



and a direct comparison has not yet been possible. But if, in the perfect state, the dif- 

 ferences are less obvious, (though, to me, they seem striking enough to justify the spe- 

 cific distinction,) there is such abundant evidence obtained by a comparison of the 

 polypoid generation, in which the tentacles and ovarian bunches, as well as the form and 

 ramifications of the stem, are so different, as to leave no doubt of the specific distinction 

 between the European and North American Corynse. However different or similar these 

 species may therefore appear to different observers, so much is plain from what we know 

 at present about them, that they are close representatives of each other in the two conti- 

 nents, and that, whether viewed as distinct species or as climatic varieties of the same 

 species, we have to acknowledge in them either those limits of variations which occur 

 between climatic varieties of the same species, or that degree of close affinity which we 

 recognize in specific representatives of the same types in analogous climates. 



Having satisfied myself of the specific distinction of the European and North Amer- 

 ican species alluded to above, I shall designate the American under the name of Sarsia 

 mirabilis, intending to express by that specific name both the w-onderful changes which 

 this species undergoes in its metamorphoses, and my admiration of the keen observer who 

 led the way in these investigations, and whose name I should have been most anx- 

 ious to retain as the generic appellation of this type, were it not contrary to the most 

 desirable improvement of our nomenclature. 



Sarsia mirabilis in its polypoid form occurs at the bottom of Boston Harbour, and 

 is never seen exposed, even at low water. I have obtained it only by dredging. In its 

 Medusa form it begins to be freed early in spring, and is very abundant along the wharves 

 all round Boston Harbour. When first freed from its polyp-like stem, the bell-shaped body 

 is about one fourth of the size to which it grows before it has again matured its eggs ; 

 when it dies, after laying them, towards the middle of summer. 



There is something quite peculiar about the duration of life of these animals, and its 

 disappearance at that particular season of the year. This connection of the animals with 

 the order and succession of the seasons is in itself very striking, and is particularly 

 evinced in the lower animals, in which the duration of life itself is dependent upon the 

 duration of the year and its changes, while in higher animals certain phenomena of life 

 recur regularly at given periods, though their longevity seems to be more and more inde- 

 pendent of the duration of the year and the influence of the season as they belong to 

 higher and higher types. In Medusae, we have not only a direct dependence of these 

 animals upon the season for their appearance, but the length of their life is actually 

 limited by the duration of the year ; and they are as much dependent upon the sea- 

 sons for their existence as most plants, or as some of the insects. They pass the 



