84 J. F. McCLENDON. 



PLATE III. 



(In Figs. 31, 32 and 33 the derivatives of a, b, c and d are separated by heavy 

 lines. ) 



FIG. 31. Sixteen cell stage. The cells of the animal-pole-side are shown by dotted 

 lines, a 3 - 1 , b 5 - 1 and b ^- 2 are in the metaphase of the fifth cleavage. 



FIG. 32. Thirty two cell stage. The cells of the animal-pole-side are shown by 

 spaced lines. 



FIG. 33. Sixty two cell stage. The primary entoblast, d 6 - 1 , and the primary 

 germ cell, d 6 - 2 , have not begun the sixth cleavage while fz' 7 - 10 , d 1 - 11 and d 1 ^ 2 are in 

 the metaphase or anaphase of the seventh. 



[Figs. 34-36, The Dichelestid. Both embryos seen from ventral (vegefal) side.} 



FIG. 34. A later stage than the one shown in Fig. 36, B, Plate VI. The pri- 

 mary entoblast cell is dividing. The primary germ cell (,v } has grown to large size 

 and the blastoderm is beginning to grow over it. At the sides of the figure some 

 mesoblast cells have been turned under the rim of the blastopore (/ 2 + 3 ). 



FIG. 35. A later stage than Fig. 34. The entoblast is in the telophase of the second 

 division. The yolk is cut through completely by both divisions of the entoblast. The 

 primary germ cell has divided (g) and the blastoderm has grown over it. 



FIG. 36. Hemispherical eggs from the ends of egg strings. 



A. Dorsal view. 



B. Anterior view. 



C. Lateral view of stage in which the blastoderm (stippled) has covered half the 

 yolk ; the entoblast nuclei are stippled heavily. 



(Figs. 4956, Panda i us simialus. ) 



FIG. 49. Sagittal section of gastrula just before the closure of the blastopore (/;). 

 ^= first polar body. ;/> = acell of the post nauplius mesoblast. a- is taken from 

 another section of the same series and shows a small cell budded off into the yolk 

 from an ectoderm cell, g is from one of the same series of sections near the median 

 line, and represents a germ cell in its relation to the ectoderm. 



FIG. 50. Part of a median cross-section of an embryo of stage C (Fig. 44). The 

 section passes through two germ cells (g) a muscle cell (in) and two entoblast 

 nuclei. The thickened portion of the ectoderm on the ventral side is the gang! ionic 

 rudiment of the second antenna. 



FIG. 51. The nauplius just hatched. The ventral aspect is shown in the left, the 

 dorsal in the right half of the figure. The median eye is seen at am, and the stomo- 

 daeum at a. The rudiments of the post nauplius ganglia (w 5 - 10 ) and appendages 

 (w r '- in ) are clearly differentiated. The entoblasts (en) are still scattered through 

 the yolk. 



FiG. 52. Section of one of the four germ cells of the nauplius showing the sixteen 

 chromosomes. 



FIG. 53. Enlarged view of section of divided cell from rim of blastopore in Fig. 

 40. All the chromosomes are not included in the section. 



FIG. 54. Prophase from same region. 



FiG. 55. Telophase. 



FIG. 56. Cross-section through germ cells, ventral ganglia, and ectoderm of nauplius 

 twenty-four hours after hatching. 



