106 



ACALEPIIS IN GENERAL. 



Part I. 



single di^ik, as in Fiij. 13. Those free disks are genuine Medusa^ and have long 

 been known as Ephyriv (PI. XP). — Flg^. OS, 50, and 00, below, represent a sunnnary 

 history of this mode of reproduction. — The Epliyrai are, in course of time, trans- 

 formed into common Medusa3 : those of our Aurelia Havidula, Per. and LeS., Fig. GO, 

 assume the characters of that genus, consisting in innumeral)le small tentacles all 

 along the margin of the disk, with four long, pendent so-called arms around the 

 mouth, etc. (comp. Plates VI., VII., and VIII.) ; while those of Cyanea arctica, which 

 at first hardly difier from those of Aurelia, are transformed into the largest Jelly- 

 fish of our coast, and end in having the appearance (if PI. III., 111.% IV., and Y. 



Fit], bt 



Fig. 59. 



F'ig. 60. 



Scyphostoma of 



AUREUA FLAVIDL'LA, Pt^r. & LeS. 



In this stage of growtli, Aurelia is 

 simply a Hydniid. 



Strobila of 



Al.ltELIA FLAVIDULA, Per. & LcS. 



o Scyphostoma reproduced at tbc luxsc 

 of a Strobila bb, all the disks of which 

 have dropped off but the last. 



Epliyra of 



AlT.ELIA FLAVIDL'LA, Vi'v. ik LeS. 



c Mouth. — If Eyes.— (.u Ovaries.— 

 n- w Tentacular spaces. 



We have thus a complete nieta})ioi'pltom of an Eplif/roiil aniinal into a perfect Mednm 

 entirely diffl'rent from it both in form and comiilication of structure, and this 

 metamorphosis is the serjuel of another seines of genetic phenomena, during which 

 one single being arising from an egg of Aurelia or Cyanea, at first free and after- 

 wards attached, ends in. dividing into a dozen and more, mag t>c twenty and more, distinct 

 free Epihgrcc, without ceasing to live, for the Strobila reproduces tentacles below 

 the last Ephyra [Fig. 50) Ijelbre this drops ofij and resumes its Scyphostoma or 

 Hydra form. Now, this part of the process is neither a metamorphosis proper nor 

 an alternate generation comjjaraljle to that of the ordinary Ilydroids, for here the 

 body of the Hydra is partially lost in the Ibrmation of the Ephyra\ The crown, 

 or row of tent;icles, at its actinal end, after separating, dies and decomposes ; while 

 the central portion of the Hydra, intermediate between the tentacles and its 

 abactinal end, divides into numerous free, active Ephyra^ which continue to live 

 until they have completed their metamorphosis, and laid an immense nund^er of 

 eggs. The base of the Hydra, with its new tentacles, also survives, and may live 

 for years. Its further history, to which I shall allude again hereafter, still presents, 

 however, some mystery. 



In the Ilydroids proper, whicli also produce free INIedusa^ the origin of the 

 free I:)rood is entirely different, and truly leads to a succession of alternate gener- 

 ations. Arising from the eggs of their free Medusa\ these Ilydroids. when matiu'e. 



