30 EMBRYOLOGICAL MONOGRAPHS. 
18-19. Optical sections showing a segmentation cavity. After fig. 20 is reached, the outer wall (epiblast ?) — 
there is but a single wall to the blastosphere—of the blastosphere folds inward, forming in Chryswora 
a gastrula. 
21-49, from Agassiz, op. cit., Vol. III. Pl. X. figs. 4, 4°, 10, 10°, 12, 14, 14%, 14°, 19, 26, 35, 368; Pl. X*. figs. 
2, 4, 10; 11, 18, 19, 22) 25, 28; Plo XT. 6; 195.20) 29°; Pl. XI*. figs. 5; 10; 16) 17; 20: 
21-33. Development of the Scyphostoma from the planula. - 
21. Planula of Aurelia. 
22. Pyriform planula with a blastopore (b/p.), In Chrysaora, according to Claus, 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 the blastopore. 
23. Still more elongated planula, resembling that of the Hydroida. blp. Blastopore. yp. Posterior pole. 
24. The planula has attached itself at 8, and beginnings of several organs of the Seyphostoma have appeared. 
blip. Blastopore. eb. Epiblast. ga. Stomach cavity known as stomodeum. hb. Hypoblast (In Chrys- 
aora infolded epiblast of the blastosphere forms the hypoblast), whose origin in this genus is unknown. 
ta. Tentacles. 
25-26. Two other attached planule. Fig. 25 has a wide-open blastopore (J p) leading into the stomach (ga), 
and fig. 26 retains its cilia. y. Ring of perisare at the base of attachment. 
27. Fixed larva with two tentacles (f71) and mouth (iJ p). ¢b. Epiblast. 2b. Hypoblast. 
28. An abnormal attached larva. b/p. Blastopore. eb. Epiblast. ga. Stomach. hb. Hypoblast. £8. Base of 
attachment. 
29. Scyphostoma with fourtentacles. 7p. Mouth. ga. Stomach. fa.! Tentacles. In Chrysaora, between this 
stage and a following, there form in the cavity of the stomodeum in intermediate planes as respects the 
tentacles four ridges, thickenings of the hypoblast, which grow in such a way as to divide the cavity into 
four chambers, as in a young Actinozoan. 
30. Older Scyphostoma. 7p, Mouth. eb. Epiblast. 2b. Hypoblast. £8. Basal attachment. Tentacles proba- 
bly solid hypoblast. 
81. Scyphostoma with eight tentacles. @2p. Mouth. eb. Epiblast. ga. Stomach. hb. Hypoblast. B. At- 
tachment. yy. Perisare. 
32. Seyphostoma with mouth (or!) mounted on a protuberance rising in the midst of the circle of tentacles (ta!). 
The oral region is bent over towards the observer, in order to show the oral prominence. 
32.1 Nematocyst from tentacle. 
33. Scyphostoma seen from the side. b2p. Mouth. 
34-40. Development of the Ephyra from the Strobila. : 
34. A Strobila with its first constriction (con }). 
34!. Attached larva with a bud (gm) from its base. 
35. A larva beginning its second constriction (con?). con.1 First constriction. 1-2. Disks constricted from the 
Strobila, later to separate from the fixed larva as Ephyre. 
36. A larva beginning a third constriction (con®). con.1 First constriction. 1-3. Constricteddisks. ta.1 Ten- 
tacles. 8. Base of attachment, and appendages near by. 
36’. A deformed Strobila. 
87. Upper portion of a Strobila with five constrictions (1-5). ocy. Otocysts(?). 07. Mouth. "py. gm. Bud from 
the side of the body. ta. Tentacle. 8. Base near attachment. 
88. Showing a Strobila just breaking its attachment of the Ephyra, whose umbrella (zr) is reversed. The 
axial attachment (man) becomes the manubrium of the Ephyra below it. 1-3. Three attached Ephyre. 
or. Mouth. {a/. Tentacles not the same as ta (fig. 27). 8. Base. 
39. A Strobila with its second row of tentacles (¢a’) present and the transitory tentacles of the Seyphostoma 
dropped. There are 13 (1-13) constricted disks, of which the upper (1) is che oldest. ocy. Otocyst. ocy. 
1b. Otocyst lobe. ta. Position of future tentacle. fa’. Second set of ten’acles. 8. Base. 
40-49. The Ephyra. 
’ 
40. An Ephyra in youngest condition, derived from a strobila with ‘false’? deciduons tentacles, and probably 
the first disk to fall off. ocy. Otoeyst. ory. 7b. Otoeyst lobe. ta. The longer of the appendages marked 
ta is probably a ‘‘ false” tentacle, which has not yet fallen off. The other may be the true Ephyra tentacle, 
ubr, Umbrella. 
41, Profile view of an Ephyra in which the mouth (or) with its lips, and the veil (ve/)? are well developed, 
man. Manubrium. ocy. Otocyst. ubr. Umbrella. 
