Flozverlike Forms and Fantasies i'] S 



which It is attached, and this gives rise to the upright 

 pedicels bearing the nutritive and the reproductive or- 

 gans, or zooids. In Obelia (Obelia commissuralis) ^ 

 however, a campanularian generally found in company 

 with Clytia, the form of growth differs considerably. 

 Here the main stem rises to a height of six inches; 

 It carries branches spirally arranged around its axis, and 

 these In turn subdivide Into other and shorter members. 

 The ultimate branches are in reality the ringed pedicels 

 of twelve-sided cups. The cups are bell-shaped but 

 slightly incurved. Indeed, the campanularlans get their 

 name from the characteristic shape of the hydrotheca, 

 for campanula, from which the name Is derived, is liter- 

 ally "a little bell." The reproductive zooids, larger 

 and vaselike, are on short, ringed pedicels occupying 

 the angles of the branches. 



Now, although the campanularlans just described 

 have a superficial resemblance, even under the glass, to 

 the sertularians, it is here in their outward aspect that 

 their similarity ceases. Their life histories are totally 

 different. In the life cycle of these hydroids is ex- 

 hibited that peculiar phenomenon known as alternation 

 of generation {metagenesis) ^ two different forms of 

 individuals In one species, or, to put it another way, one 

 kind of individual in two separate and distinct forms. 

 Specifically, Clytia and Obelia are at one stage of their 

 lives fixed hydroids, or polyps; at another, jellyfishes. 



Here is how It comes about. The reproductive 

 zooids of these animals, unlike those of the sertularians, 

 produce neither eggs nor sperms; Instead, they contain 

 little stacks of saucer-shaped meduscC, or jellyfishes, 

 which, in their form of attachment to one another by 



