584 CELL DIVISION IN EGGS OF CREPIDULA. 



PLATE XLV. 



Cleavage of Isolated Blastomeres. 



Fig. 30. Exp. 906: Third cleavage in i or f blastomeres, separated by pressure; the cells are 



normal macromeres, owing 



positions of spindles and cytoplasmic 



cells have undergone certain changes as may be seen by comparison with 

 Fig. 31. Exp. 921: \ or f 



normal 



though division in B has been delayed. . 



Fig. 32. Exp. 855: i blastomere, isolated by shaking; the nrst micromere has been formed and 

 the second is forming in typical manner. Original animal pole indicated by polar bodies. 



Fig 33. Exp. 855: \ blastomere, isolated by shaking ; the first and second micromeres have formed 

 in normal manner, and the former is dividing as in a whole egg. Original animal pole indicated by polar 



° Fig. 34. No. 714: £ blastomeres, probably separated by pressure; each macromere has given off a 

 micromere in dexiotropic direction, as in whole eggs. . 



Fig 35 Exp. 855: £ or f blastomeres, separated by shaking; each has produced a first micromere 

 in dexiotropic and a second in Inotropic direction, and the former are dividing in lseotropic direction just 

 as in whole eggs. The micromere plate is a continuous one, without breaks. 



Fig 36. No. 711: f blastomeres, one macromere having been separated, probably by pressure. 



has formed one micromere in normal fashion, but a gap exists between micromeres 



and la. 



Fig 37 Exp. 864: \ or f blastomeres, separated Dy nypertonic sea water ana tnen leit in normal 

 sea water 10 hrs Each macromere has formed three micromeres, and the first and second of these have 

 subdivided in normal fashion. The egg is a whole in the sense only that it shows no gaps where cells are 



missing 



Fig. 38. No. 715: \ egg, probably separated by pressure after third cleavage, as shown 



micromeres 



micromere 



two micromeres oi tue iusi act \lu, <m<a ±v, »iv ^v^~~v. . , 



Fig 39 Exp. 875: f blastomeres, macromere C having been destroyed in dilute sea water, the 

 m™rp«'lm™ Viven off the first micromeres, and these have subdivided in typical fashion, forming a 



Fig. 40. Exp. 958: f blastomeres, separated by shaking. Cells A and D have given rise to first 

 and second micromeres in normal manner; B has formed only the first micromere and both IB and 16 lack 



nUCl FiG. 41. Exp. 867: f blastomeres, separated in hypertonic sea water. Typical cleavage of micro- 

 meres and macromeres of each quadrant represented, but the cells of one quadrant are wholly ; lacking 



Fig 42. Exp. 1002 (2) : f blastomeres, separated by pressure. Cleavage typical for each quadrant, 

 but delayed in quadrant B; the third micromere is just coming off from 2D. nna drants 



Fig. 43. Exp. 958: f blastomeres, separated by shaking.^ ^^^<fj£? 2^2™! 

 A, C, and D is absolutely typical, 

 gaps to mark the places from which they have dropped out. 



micro- 



naTesandTn adclmoTl) 1 las "given rise' to a fourth, the mesentoblast 4d( " ^^£ "^ 



'■■•--■ ied in typical manner, giving rise to a cross (stipp ed cells) with three a^s mstead « lour 



Exp. 959: f blastomeres separated by shaking; the cleavage of each macromere and tne 



Fig. 44. 



subdivisions of each micromere have taken place as in normal 



PLATE XLVI. 



Effects of Pressure 



Fig. 45. 



Fig. 46. Exp 



Exp. 918: Egg pressed during formation of seeond polar _body wMeh is a—^ 



leavage 



lobulated. 



Fig. 47. Exp 



Similar 



Fig. 48. 

 Fig. 49. 



Exp. 901: Very large yolk lobe at vegetal pole ot one oi tne ""*»• ..*& abnormally 



No 724 : Egg probably pressed during the first cleavage ; second cleavage spindles aono 



small. 



Fig. 50. Exp. 918: Pressed during second cleavage 



normallv giving rise to micromeres 



ill incomplete, and the entire amphiaster is abnormally large. multifile nuclei formed 



Fig. 51 Exp. 911: Pressed during the first cleavage; three macromeres with multiple nu 



tn aster 



Fig. 52. Exp. 91 

 with their micromeres 



y second and third cleavages in chief axis oi egg; ^^^f Jjjies 

 normal ; macromeres A and B have divided in abnormal p 



Exp. 911: Pressed during second and third cleavages ^ r c ^ ef „ a ^ S Q 2 . W'» iCandlZ* 

 c are abnormally large and are dividing like micromeres of the nrst set , in * , 

 vision is like that in the formation of the 2d set of micromeres. 



