Germ Cells and early Embryology of certain Aphids. 641 
Fig. 46. Long. section of the posterior part of a sexual ovum, 
showing the entering of follicular cells from the follicular walls of the 
oviduct which form the secondary yolk. 
Fig. 47. Transverse section of the extreme posterior end of sexual 
ovum, showing the transformation of the follicular cells into the secondary 
yolk. /. ¢ folliculor cells, s. y secondary yolk. 
Fig. 48. Transverse section of a single ovarian gland. / karyosomes, 
cy cytoplasm, ch chromatin with denser portion of nucleoplasm. 
Fig. 49. Long. section of posterior end of ovum, with the early 
proliferation of the blastoderm cells. bi. ¢ blastoderm cells, s. y secondary 
yolk, y. s yolk spheres or primary yolk. 
Fig. 50. Long section of sexual developing embryo at the beginning 
of gastrulation. bl blastoderm, s. y secondary yolk. 
Fig. 51. Longitudinal section of developing embryo when the germ 
band is entirely immersed and separated from uninvaginated part of the 
blastoderm. s serosa, g. b germ band, am part of the germ band which 
becomes the amnion, s. y secondary yolk. 
Pilate: 52. 
Fig. 52. Long. section of posterior end of egg, showing the portion 
of the blastoderm which becomes the germ band during gastrulation. bl 
blastoderm, s. y secondary yolk, s serosa. 
Fig. 53. Long. section of egg with male and female pronucleus 
before fusion. 
Fig. 53a. Pronuclei a little later than preceding. 
Fig. 54a. Fusion of nucleoplasm and periplasm. np nucleoplasm, 
pr periplasm, p. bs polar bodies, prn pronucleus. 
Fig. 54—60. Cleavage and formation of the blastoderm. Ci. ¢ 
cleavage cells, s. 7 secondary yolk, y.n yolk nuclei derived from cleavage 
cells, bl blastoderm. 
Fig. 61. Stage a little later than preceding showing the beginning 
of the proliferation of blastoderm cells at the posterior pole. 
Plate 53. 
Fig. 62—74. Spermatogonia before and after the last spermatogonial 
division. 
Fig. 75—80. Growth of spermatogonia and formation of spireme. 
Fig. 81—97. Formation of chromosomes and first spermatocytic 
division. 
Fig. 98—106. Second spermatocytic division. 
Fig. 107—110. Spermatids at the beginning of transformation period. 
