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THE POPULAR SCIENCE MONTHLY. 



primitive than their more complex manifestations, and all analogy- 

 forces us to believe that Dysmorphosa is the descendant of some 

 remote ancestor whose life-history was as simple and direct as that 

 of a bird or a mammal or a frog, a butterfly, a snail, a crab, or a 

 star-fish, and that originally each ^g^ became converted into an 

 adult by growth and metamorphosis. 



If this is true, how has its complexity arisen ? What were 

 the stages in the gradual acquisition of the life-history which is 

 shown in our diagram ? What forces have produced the change, 

 and what is its significance or advantage ? 



Not very long ago such questions were held to be unanswerable 

 and meaningless, but at the present day we are all familiar with 

 the process of reading the past history of life by the study of 

 comparative anatomy and embryology, and are ready to accept 

 the evidence of the series of living hydroids which show us the 

 character of the changes through which the ancestors of Dysmor- 

 phosa have passed, as they have gradually acquired the structure 

 which is exhibited by their living descendants. 



I shall now briefly describe a few American species of jelly- 

 fish, which exhibit successive stages in the process of complication, 



and serve to show that the 

 remote ancestor of Dysmor- 

 phosa must have been a 

 jelly-fish, which passed, dur- 

 ing its development, through 

 a transitory larval hydra 

 stage, which was only a step 

 in the process of growth of 

 the embryo into an adult. 

 In this form each egg pro- 

 duced one animal ; the adult 

 life was all -important, and 

 the hydra stage was passed 

 as quickly as possible ; and 

 during the history of the 

 species this has gradually 

 become a more and more important part of the whole life, until 

 finally the adult jelly-fish has become comparatively unimportant 

 and simply serves to secure the distribution of the species, while 

 the larvae have acquired the power to bud and to build up colonies, 

 the members of which have become specialized in various direc- 

 tions, by division of labor, for the benefit of the whole. 



One of the most graceful MeduscB of our Southern coast, from 

 Florida to the Chesapeake Bay, is the beautiful Liriope shown, 

 somewhat enlarged, in Fig. 2. It is not very different from Dys- 

 morphosa in shape, but it is much larger, and a most active and 



Fia. 6.— Hydra sta^e of the larva of Liriope ; 

 ach ; c, mouth ; /, tentacles. 



d, stem- 



