38 EXPLANATION OF THE PLATES. 



PLATE XXI. 

 Figs. 40-03 = Optica] sections. X 120. 



Fig. 40. An unfertilized egg a few moments after deposit. This was a well-matured egg, in which the 

 granules were relatively few. The granules are confined to the periblast, and are here repre- 

 sented as they appeared in surface view. 



Figs. 41-52. Successive views of another egg, taken at intervals of five minutes. This egg did not cleave, 

 but the disc formation aud the attendant phenomena are the same as have been seen many 

 times in eggs that developed normally. Fig. 41, the first of the series, shows a stage five 

 minutes after fertilization. 



Figs. 53-63. This egg was taken from the sea ; aud the first view (Fig. 53) represents a stage about thirty 

 minutes after fertilization, in which two polar globules are present, and the pronuclei are in 

 the condition shown in Fig. 4 a. Assuming that Fig. 53 represents a stage of thirty minutes, 

 the times of the following views will be : — 



Fig. 54 = 35 minutes. Fig. 59 = 53 minutes. 

 " 55 = 40 " " 00 = 55 



" 56 = 43 " " 01 = 05 " 



" 57 = 45 " " 02 = 70 •' 



" 58 = 50 " " 03 = 75 



Dotted hue in Figs. 61-63 shows the niveau of the yolk sphere. 



PLATE XXII. 



Figs. 1-7- Surface views immediately after fertilization, showing the micropyle, the archiamphiaster (first 

 polar spindle), and a variously shaped body supposed to be the spermatosome. The position 

 of the micropyle with respect to the archiamphiaster is seen to lie variable. X 280. 



Figs. 8, 9. Successive sections of the preparation shown in Fig. 6. The spindle is short aud vertical The 

 doubtful spermatosome is shown in Fig 11. attached to tiie membrane, and hence it is uncer- 

 tain whether it lias actually penetrated the egg. X 2S0. 



Fig. 10. Another directive spindle of same time, but a little longer, and more sharply defined. X 280. 



Figs. 11, 12. The same spindle from the side and end. X 1060. 



Fig. 13. Surface view of blasfodisc ten minutes after fertilization, showing the male pronucleus, the first 

 polar globule, and the polar spindle. X 280. 



Fig. 14. Twenty minutes after fertilization. Second polar spindle has divided ; female pronucleus on its 

 way to join the male pronucleus. X 280. 



F'igs. 15, 16. Of the same age, but the pronuclei nearer together. X 280. 



Figs. 17, 18. Sections of two eggs from the sea, supposed to be about twenty minutes after fertilization. 

 The male pronucleus lies in deeper part of the disc, below the female pronucleus, in Fig. 18. 

 In F'ig. 17 the 9 pronucleus lies to the left of the <J pronucleus. X 280. 



Figs. 19, 20. Successive sections of a disc twenty minutes after fertilization. The two nuclei are approach- 

 ing each other in a nearly horizontal plane. The disc is much thinner than in Fig. IS, and the 

 relative position of the nuclei may account for the difference. X 280. 



PLATE XXII 1. 

 Magnification = 280. 



Figs. 21-23. Surface views of hlastodisc thirty minutes after fertilization, p, polar globule; p/i, pronuclei. 



Figs. 24-26. Successive sections of a blastodisc twenty minutes after fertilization. 



Fig. 27- Optical section of the first spindle and polar globule ten minutes after fertilization. 



Fig. 28. A section passing through the micropyle and the spermatic? body a few seconds after fertilization. 



m. micropyle. 

 Figs. 29, 30. Sections of two blastodiscs. each thirty minutes after fertilization. 

 Figs. 31, 3.3, 34. Surface views forty minutes after fertilization. 

 Fig. 32. Vertical section of a disc of same age. 



