1904.J NATURAL SCIENCES OF PHILADELPHIA. 403 



Plate 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 showTi in figs. 17 

 and 18 are fulh' completed. 2-4 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 Iseotropically, 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 Iteotropic 

 division of 3D, forming 4D and 4d (ME), is completed. 



Fig. 23. — Animal pole view of egg containing 41—14 cells, la'-ld' have 

 divided in a dexiotropic direction the "apicals" (la"-ld") and the 

 "basals" (la'--ld'-) of the" ectoblastic cross." 



Plate XXIV, Fig. 24. — Same egg as fig. 23, seen from vegetative pole. All 

 tlie third quartet cells have divided Iseo tropically. 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 meseutomere 

 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) heotropic division of 2b-' ; Iseotropic to horizontal 

 division of 2c-'. The trochoblasts, Ic-, Id-, are also beginning to 

 divide. 



Fig. 29. — Same egg as fig. 2S, seen laterally from B cjuadrant. 



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'. 



Plate 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, shownng cleavage in three 

 of the "basal" cells of the cross, lb'- is dividing in a la?otropic 

 direction; in Ic'^ the spindle is dexiotropic to radial in position; in 

 la'- heotropic to radial spindle. The turrets, la- and lb', show dexio- 

 tropic cleavage. About 60 cells. 



Fig. 34. — Mew of vegetative pole of somewhat older stage than fig. 31 ; 

 3a', 3a^, 3b' and 3Vj- liave 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. — L^pper pole view^, showing completion of cleavage forming " l^asals" 

 (la'^'-ld'2') and "middle" (la'^^-ld'-) cells of cross. 



Fig. 40. — Slightl}^ older stage than preceding, .showing completed cleavage 

 of 3b'. 



Fig. 41. — Same egg as fig. 40, A cjuadrant. 



Plate XXVI, Fig. 42. — View of vegetative pole of egg with about 68 bias- 

 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 Iseotropic divisions in 

 3d", 3d'^ 



Fig. 44. — Same egg as fig. 43, seen from C cjuadrant. 3c" and 3c'^ are divid- 

 ing dexiotropically. 



Fig. 45. — View of vegetative surface of egg with about 80 cells. The 

 mesentomeres have cHvided 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. 



