30 EMBEYOLOGICAL MONOGRAPHS. 



18-19. Optical sections sliowing a segmentation cavitj'. After fig. 20 is reaclieil, the outer wall (cpiWast?) — 

 there is hut a single wall to the blastosphere — of the blastosphere fohls inward, forming iu Chrysaora 

 a gastrula. 



21-49, from Agassiz, op. cit., Vol. III. PI. X. figs. 4, 4°, 10, 10>, 12, 14, 14", 14«, 19, 26, 35, 36" ; V\. X». figs. 

 2, 4, 10, 11, 13, 19, 22, 25, 28 ; V\. XI. 6, 19, 20, 29 ; PI. XI'. figs. 5, 10, 16, 17, 20. 



21-33. Development of the Scyphostoma from the planula. 



21. Planula of vfi(rc/i'a. 



22. Pyriforni planula with a blastopore (blp.). In Chri/naora, according to C'laas, after the formation of the gas- 



trula the blastopore closes, forming a closed sac. In Agassiz's figures it remains open, and forms the mouth 

 of the Scyphostoma. The relationship of the mouth and inner cavity of the gastrula remains doubtful. 

 p. Pole opposite tlie blastopore. 



23. Still more elongated planula, resembling that of the Hijdroida. hip. Blastopore. ;;. Posterior pole. 



24. The planula has attached itself at /3, and beginnings of several organs of the Scyphostoma have appeared. 



hip. Blastopore, ch. Epiblast. ga. Stomach cavity known as stomodasum. hb. Hypoblast (In Clirys- 

 aora infolded epiblast of the blastosphere forms the hypoblast), whose origin in this genus is unknown. 

 ta. Tentacles. 

 25-26. Two other attached planvila;. Fig. 25 has a wide-open bl.astopore (Up) leading into the stomach (ijn), 

 and fig. 26 retains its cilia. 7. Piing of jierisare at the base of .attachment. 



27. Fixed larva with two tentacles (^e') and mouth (lilp). ch. F.piblast. lib. Hypoblast. 



28. An abnormal attaelied larva, hljj. Bl.astopore. eh. Epiblast. (ja. Stomach, hb. Hypobkst. /3. Base of 



attachment. 



29. Scyphostoma with four tentacles, blp. Jlonth. 31.. Stomach, ta.'^ Tentacles. In Cliri/snorn, between this 



stage and a following, there form iu the cavity of the stomoda;um in intermediate planes as respects the 

 tentacles four ridges, thickening.s of the hypoblast, which grow in such a way as to divide the cavity into 

 four chambers, as in a young Aetinozoan. 



30. Older Scyphostoma. blp. Mouth, c h. Epiblast. h b. Hypoblast. /3. Basal attachment. Tentacles proba- 



bly solid hypoblast. 



31. Scyphostoma with eight tentacles. Up. Month, c h. Epiblast. ga. Stomach, h h. Hypoblast. /3. At- 



tachment. 7. Perisare. 



32. Scyphostoma with mouth (ofi) mounted on a protuberance rising in the midst of the circle of tentacles (<«'). 



The oral region is bent over towards the observer, in order to show the oral prominence. 

 32.' Nematocyst from tentacle. 



33. Scyphostoma seen from the side, hi p. Mouth. 



34-40. Development of the Ephyra from the Strohila. 



34. A Strobila with its first constriction (eon '). 

 34'. Attached larva with a bud (gm) from its base. 



35. A larva beginning its second constriction (con"), con.^ First constriction. 1-2. Disks constricted from the 



Sti'obila, later to separate from the fi.xed larva as E]ihjTa!. 



36. A larva beginning a third constriction (con 3). roji.i First constriction. 1-3. Constricted disks, te.' Ten- 



tacles, p. Base of attachment, and appendages near by. 

 38'. A deformed Strobila. 

 87. Upper portion of a Strobila with five constrictions (1-5). oc;/. Otocysts(?). or. Mouth. P'J. gm. Bud from 



the side of the body. ta. Tentacle. /3. Base near attachment. 



38. Showing a Strobila just breaking its attachment of the Epliyra, whose umbrella (iihr) is reversed. Tlic 



axial attachment (man) becomes the manubrium of the Ephyra below it. 1-3. Three attached Ephyra?. 

 or. Month, ta'. Tentacles not the Siime as la [fig. 27). |8. Base. 



39. A Strobila with its second row of tentacles (/((') present and tlie transitory tentacles of the Scyphostoma 



droppi^d. There are 13 (1-13) constricted disks, of whicli the upper (1) is die oldest, ooj. Otoeyst. cy. 

 lb. Otoeyst lobe. ta. Position of future tentacle, la'. Second set of ten'.acles. ^. Base. 



40-49. The Ejibyra. 



40. An Ephyra in youngest condition, derived from a strobila with "false" deciduous tentacles, and probably 



the first disk to fall olf. or?/. Otocy.st. cry. /6. Otocy.st lobe. ta. The longer of the appendages marked 

 to is iirobaldy a " false" tentacle, wliidi lias not yet fallen off. The other may be the ti-ue Ephyra tentacle. 

 ubr. Umbrella. 



41. Profile view of an Ephyra in which the mouth (")) with its lips, and the veil {vil) 1 are -well developed. 



■)nan. Manubrium, ocy. Otoeyst. ubr. Umbrella. 



