PLATE XIII. 



Tig. 50. —Circulatory apparatus, (ii<^estive tract, and one of the segmental 

 organs. MnniiiGeti circa 50 diain. (li days old.) 



Fig. 57- — A transverse section of tlie egg-string, showing the central 

 nucleated protaplasm (rhachis) and the j>eriplieral layer of primitiye egg- 

 cells. Magnified 440 diam. 



Fig. 58. — A iDngitudinal, optical section of the egg-string, a, b,c, and 

 rf = buccesbive stages in the growth of the egg-cell. The rhacliis is liere 

 much larger comparatively than in Gg. 57. Maguified 16) diaui. 



Fig 59. — A portion ol the egg-string at a time when the eggs have come 

 to lie externally to it. Magnified 50 diam. 



Fig. go. — Tliree vesicula; gcrminativic. a represents the vesicle at the 

 time the egg is liberated from the string, h is the vesicle of the full-grovva 

 egg, and c is probahly an iiici[tient reticular stage. Magnified IGO diam. 



Fjg. G1. — Kucleus corres|)Ouding nearly wiih the stage represeuied iu 

 fig. 58. Tlie liomogeneous nucleolus lies in the centre of the reticulum. 

 Magnified 440 diam. 



Fig. 62. — Section of a fresh-laid egg, showing the archiamphiaster. Only 

 a part of the section is represented. xVlagnified 160 diam. 



Fig. 63. — The second polar globule is iu process of elimination. Magni- 

 fied 160 diam. 



Fig. 64. —One pole of the amphiaster in fig. 62 more highly magnified. 

 (410 diam.). 



Fig. 65. — A. Section of the egg just after the formation of the polar 

 globules. The male {m.P/i) and female {f-Pn) pronuclei are present. 

 Magnified 50 diam. 



B, The polar globules highly magnified. (Zeiss J. and the camera 

 iiach (Jberhiiuser.) 



Fig. G6. — C is a section of the egg at the time the first polar ring begins 

 to form. The pronuclei are approaching each other. In the female pro- 

 nucleus two pronucleoli are seen in close contact. The same are more 

 highly magnified in D. The male pronucleus (magnified 160 diam. iu E) 

 contains only one nucleolus. F re[)resents the united pronuclei. 



Fig. 67. — G is a section of the egg just alter the union of the pronuclei. 

 The |)atli of the female pronucleus is indicated by the shaded line. Mag- 

 nified 50 diam. 11 and 1 are two primary cleavage-nuclei. Magnified 160 

 diam. 



PLATE XIV. 



Fig. 68.— K is a section of the egg thirty minutes after the appearance 

 of the first polar ring. The second ring already covers tlie lower pole. L 

 repre.sent,s the cleavage-nucleus of another section. Magnified 160 diam. 

 N = the three pronucleoli. 



FiG.s. 69, 70. and 71 (Oj represent sections of the egg forty-five minutes, 

 sixty minutes, and sixty minutes respectively after the appearance of the 

 first polar ring, showing the concentration ol the rings. In fig. 71 (O) the 

 nuchms is spindle-shaped, but ilie nucleoli are still unchanged. P is another 

 nucleus of the same date, magnified 160 diam. 



]<'i,j 72 — The nucleus has assumed the am()hiastral form, and the ring- 

 substance has plunged decjjer into the egL'. This section b. ars the same 

 date as figs. 70 and 71, but is evidently farther advanced. Magnified 50 

 diam. 



Fig. 73.— a little farther advanced than fig. 72, although of the same 

 date. Magnified 50 diam. 



Fig. 74. — A momenl before the fil■.^t cleavage begins. 



