IO4 EDWARD DRAKE CRABB. 



PLATE 4. 



Virgin eggs fixed in modified Flemming followed by nitric acid solution, 

 IOM, iron-hsematoxylin, Gage's acid fuchsin except Fig. 35, and reproduced 

 to the scale shown below. 



FIG. 26. From a single section showing both pronuclei. The second 

 polocyte is on the next section. 



FIG. 27. Reconstructed from two consecutive sections, showing both 

 pronuclei and second polocyte. 



FIG. 28, 29. Two consecutive sections. Fig. 28 contains the entire 

 sperm pronucleus ; Fig. 29, the entire egg pronucleus, except that some frag- 

 ments of karomeres on the next section were not transposed. A thin layer 

 of egg cytoplasm separates the two pronuclei. 



FIG. 30, 31. Two consecutive sections. Fig. 31 shows the sperm and 30, 

 the egg pronucleus. The two pronuclei are separated by a very thin layer 

 of cytoplasm. 



FIG. 32. A fertilization stage with a supernumerary sperm pronucleus. 

 Reconstructed from three consecutive sections. The first section contains 

 the second polocyte, in which the chromosome vesicles have apparently dis- 

 integrated, and the disintegrating sperm pronucleus. The egg pronucleus 

 is on the second section and the active sperm pronucleus is on the third. 



FIGS. 33, 34- Two consecutive sections. Fig. 33 shows the sperm pro- 

 nucleus and three vesicles of the egg pronucleus. In Fig. 34 the chromo- 

 somes of the first polocyte are arranged in monaster metaphase and are 

 apparently disintegrating. The second polocyte has vesicles in which the 

 chromatin is in the form of disintegrating chromomeres. A " Zwischen- 

 korper," Z, connects the cytoplasm of the ovum with that of the second 

 polocyte, as in Fig. 27. 



FIG. 35. From a single section, showing the karyomeres nearly all fused 

 to form definite pronuclei. The chromosomes of the first polocyte have 

 undergone monocentric division resulting in an indefinite number of chro- 

 matin masses. The centrosome of the monaster is distinctly visible. 

 Ohlmacher, 6 M, iron-haematoxylin. 



FIGS. 36, 37. Two of three consecutive sections. Fig. 36 shows the sperm 

 pronucleus and 37, the egg pronucleus. The intervening section shows no 

 trace of either pronucleus, but it does show that the hyaline region sur- 

 rounding the two pronuclei is continuous and practically free from yolk 

 granules as is shown in Fig. 33. 



