740 



THE POPULAR SCIENCE MONTHLY. 



THE GROWTH OF JELLY-FISHES. 



A CHAPTER IN THE NEW ZOOLOGY. 



By Peof. W. K. BEOOKS, 

 of johns hopkins univeesity. 



II. 



[Concluded.'] 



IN the first part of this article I described the life-histories of 

 two hydroids : one, Liriope, in which each egg gives rise to 

 only one jelly-fish, which is solitary and free at all stages of its 

 existence, and without any power to multiply asexually; and a 

 second species, Dysmorphosa, in which there is no limit to the 

 number of adults to which a single egg may give rise, and in 

 which the life-history is a complicated alternation of generations, 

 with a sessile polymorphic hydroid stage from which the sexual 

 jelly-fishes are produced by budding. 



I shall now briefly sketch the more prominent features in the 

 history of the process of specialization which has gradually 

 evolved a complicated life-cycle like that of Dysmorphosa from 

 one as simple and direct as that of Liriope, The parasitic jelly- 

 fishes are peculiarly instructive in this connection. The genus 

 Cunina includes a number of species which, while young, are 

 parasites on other jelly-fishes. The free-swimming adult of one 

 of them {Cunocantha odonaria) is shown in Fig. 9. It is quite 



f a. d 



FiQ. 9.— Side view of Cunocantha octonaria, slightly ma^ifled, drawn from Nature by W. K. Brooks. 



common upon the coast of Virginia and North and South Caro- 

 lina. The adult is not a parasite, but as soon as the larvae hatch 

 from the eggs they make their way into the bell of another jelly- 

 fish, and live there as parasites until they complete their develop- 

 ment and assume the adult form. The jelly-fish which affords a 

 home for these parasites is shown at k in Fig. 15. It is known as 

 Turritopsis. 



