HABITS, ETC., OF CERBBRATULUS LAOTEUS. 197 



Fig. 54. — Eight-cell stage, showing dextral twisting of the upper cells. 

 Enlarged frona camera lucida sketch of living egg. 



Fig. 55. — Blastula with differentiated ectoderm and entoderm, and mesen- 

 chyme cell separating from the latter. 3 and 7, from a preserved and mounted 

 specimen. 



Fig. 56. — Section showing nuclear spindle parallel with surface subsequent 

 to giving off of first polar body. 3 and 3. 



Fig. 57. — Same with spindle diagonal after extrusion of second polar body. 

 Fig. 58. — Same with segmentation spindle for first segmentation. 

 Fig. 59. — Sperms, enlarged from camera lucida sketch, cf. Fig. 42. 



PLATE 11. 



Fig. 60. — Longitudinal horizontal section of a regenerating papilla, showing 

 formation of sexual pouches and intestinal caeca; anus terminal. 3 and ToUes 

 1-inch objective. 



Figs. 61 and 62. — Longitudinal horizontal sections of male and female; 

 immature genital pouches scattered through the connective tissue. Killed in 

 April. 1 and 3. 



Fig. 63. — Transverse section of female killed in April, sliowing relation of 

 developing egg-pouches to inner longitudinal muscle layer. 3 and 3. 



Fig. 64. — Portion of immature ovary from Fig. 62, enlarged to show 

 method of egg development. 1 and 7. 



Fig. 65. — A single egg pouch of Fig. 62, enlarged to show egg cells, yolk 

 cells, and glycerine cells. The walls are formed from connective tissue. 

 1 and 7. 



Fig. 66. — A single sperm pouch of Fig. 61, enlarged to show formation of 

 sperm mother-cells. The connective tissue here extends into the pouch, and 

 the sperm cells are supported upon it. 3 and 3 ; tube drawn 60 mm. 



Fig. 67. — A small portion of Fig. 66, enlarged to show the way in which 

 the sperm cells are borne on the mesoderm strands. 3 and 7 ; tube drawn 

 60 mm. 



Fig. 68. — A single sperm pouch magnified still farther to show transfor- 

 mation from sperm mother-cells into sperms. 3 and one twelfth oil immer- 

 sion. 



Figs. 69 — 73. — Vertical sections of a late blastula and four gastrulas in 

 different stages of development, showing the origin and development of the 

 apical plate, the formation of mesenchyme cells, and clearing of ectoderm. 1 

 and 7 ; tube drawn 60 mm. 



VOL. 43, PART 1. NEW SERIES. 0 



