1904. } . NATURAL SCIENCES OF PHILADELPHIA. 403 
Puate XXIII, Fig. 18.—Slightly later stage (lateral view) than fig. 17. Divi- 
sion of the second quartet is about completed. 
Fig. 19.—Animal pole view of egg, in which the divisions shown in figs. 17 
and 18 are fully completed. 24 cells. 
Fig. 20.—Vegetative pole view of egg slightly older than fig. 19, showing 
spindle which initiates the separation of 4d. 
Fig. 21.—Transition stage between 25 and 33 cells (seen from animal pole). 
All eight cells of the second quartet are dividing leotropically, the 
upper four forming the “‘tip”’ cells of the cross (2a", 2b", 2c, 2d). 
Fig. 22.—Same egg as fig. 21, seen from vegetative pole. The lxotropic 
division of 3D, forming 4D and 4d (ME), is completed. 
Fig. 23.—Animal pole view of egg containing 41-44 cells. 1la!-1d' have 
divided in a dexiotropic direction the ‘‘apicals” (la!—1d") and the 
“basals” (la!’—ld”) of the“ ectoblastic cross.” 
PuaTE XXIV, Fig. 24.—Same egg as fig. 23, seen from vegetative pole. All 
the third quartet cells have divided lxotropically. The macro- 
meres, 3A, 3B, 3C, are dividing in a similar direction to complete the 
fourth quartet. 
Fig. 25.—View of vegetative pole of egg slightly older than fig. 24. The 
formation of the fourth quartet is completed and the mesentomere 
4d (ME) has divided into right (ME') and left (ME*) halves. 
Fig. 26.—Lateral view from B quadrant of an egg same stage as fig. 25. 
Fig. 27.—Lateral view of an egg, D quadrant, same stage as fig. 25. 
Fig. 28.—Animal pole view of an egg showing, (1) dexiotropic divisions of 
2c, 2a!?, 2b'?; (2) lwotropic division of 2b*!; leotropic to horizontal 
division of 2c. The trochoblasts, 1c?, 1d’, are also beginning to 
divide. 
Fig. 29.—Same egg as fig. 28, seen laterally from B quadrant. 
Fig. 30.—Same egg as fig. 28, lateral view of C quadrant; 3c! is cleaving in 
a dexiotropic direction. 
Fig. 31.—Vegetative pole view of same egg as fig. 28, showing bilateral 
divisions of 3c!, 3d’. ; 
Puate XXV, Fig. 32.—Lateral view D quadrant. slightly older stage than fig. 
28, showing bilateral divisions of 3c’, 3d’. 
Fig. 33.—Upper pole view of same egg as fig. 32, showing cleavage in three 
of the “basal” cells of the cross. 1b” is dividing in a leotropic 
direction; in 1c” the spindle is dexiotropic to radial in position; in 
la” leotropic to radial spindle. The turrets, 1a? and 1b’, show dexio- 
tropic cleavage. About 60 cells. 
Fig. 34.—View of vegetative pole of somewhat older stage than fig. 31; 
3a}, 3a7, 3b! and 3b? have all divided in a dexiotropic manner. 
Fig. 35.—Same stage as fig. 34, lateral view of C and D quadrants. 
Fig. 37.—Lateral view of A quadrant, showing dexiotropic division of 3a’. 
Fig. 38.— Upper pole view, showing completion of cleavage forming “‘basals’’ 
la!!_1d"!) and ‘‘middle”’ (1a!**-1d!”") cells of cross. 
Fig. 40.—Slightly older stage than preceding, showing completed cleavage 
of 3b! 
Fig. 41.—Same egg as fig. 40, A quadrant. 
Pirate XXVI, Fig. 42.—View of vegetative pole of egg with about 68 blas- 
tomeres. ME! and ME’ are dividing bilaterally. 
Fig. 43.—Lateral view, A and D quadrants of egg with about 75 blastomeres, 
showing dexiotropic cleavage of 2a” and leotropic divisions in 
3d", 3d”: 
Fig. 44.—Same egg as fig. 43, seen from C quadrant. 3c" and 3c” are divid- 
ing dexiotropically. 
Fig. 45.—View of vegetative surface of egg with about 80 cells. The 
mesentomeres have divided into two small cells, E' and E*, and 
two large, Me! and Me’. 
Fig. 47.—Same egg as fig. 45, lateral view of D quadrant. 
