THE AMERICAN LOBSTER. 251 



Fig. 221. Surface view of segmenting egg, under observation 5 Lours (8 p. m. to 1 a. m.). At 12 o'clock 

 the segments shown in the drawing were very convex at surface, standing far apart as if 

 the egg were breaking up. At 1 a.m. the segments were closer together and nuclei were 

 about to divide again. Drawing made at 11 p. in., after completion of division. 29 times 

 natural size. 



Fig. 222. Surface view of segmenting egg. Drawing begun at 11 a. in. ; when completed, half an hour 

 later, the nuclei had divided and segmentation furrows were making their appearance. 

 29 times natural size. 



Fig. 223. Surface view of same egg, drawn at 12 m. Division of cells mostly completed. 29 times 

 natural size. 



Fig. 224. Surface view of same egg as in figs. 222 and 223, at 9 p. m., in advanced stage of segmen- 

 tation. At 2.45 p. m. nuclei were dividing; at 6.45 p. m., when examined, division was 

 completed. Drawing made at 9 p. m. 29 times natural size. 



Fig. 225. Surface view of egg in advanced stage of yolk segmentation. Free-hand drawing. 29 times 

 natural size. 



Fig. 226. Surface view of egg in abnormal yolk segmentation, showing a larger yolk mass at the lower 

 part of the figure and a number of smaller regular segments. A similar large yolk mass 

 occurs on the opposite side of the egg next to the one shown in the drawing. 29 times 

 natural size. 



Plate 51. 



Fig. 227. Surface view of egg in invagination stage. August 3, 11.30 a. m. 29 times natural size. 



Fig. 228. Surface view of abnormal embryo in egg-nauplius stage. August 10. 29 times natural size. 



Fig. 229. Surface view of abnormal embryo. August 8. 29 times natural size. 



Fig. 230. Surface view of abnormal embryo in egg-nauplius stage. P, cells approaching surface; 

 r, outward fold of surface epithelium ; y, yolk. August 9. 29 times natural size. 



Fig. 231. Surface view of abnormal embryo in egg-nauplius stage. August 8. 29 times natural size. 



Fig. 232. Lateral view of embryo, showing large white patch behind abdomen. August 5. 29 times 

 natural size. 



Fig. 233. Lateral view of embryo about 5 weeks old, showing lateral fold of carapace covering the 

 antenna 1 , the heart (St.), the intestine containing characteristic concretions (P), the 

 telson (T) overlapping brain and optic lobes, and the lateral indentations of the yolk 

 corresponding to divisions of the midgut. July 29. 48 times natural size. 



Fig. 234. Surface view of embryo about 25 days old, showing the large optic lobes of cephalo-thoracic 

 appendages. The telson touches the brain, and the crescentic fold of the carapace 

 extends forward as far as the first maxillipeds. August 3, 1892. 29 times natural size. 



Fig. 235. Lateral view of double monster in egg-nauplius stage. August 13. 29 times natural size. 



Plate 52. 



Fig. 236. Part of transverse section of egg in stage between that shown in figs. 224 and 225, yolk cells 



(y c) being formed by tangential division. About 70 times natural size. 

 Fig. 237. Part of longitudinal section of egg in egg-nauplius stage, showing degenerating cell (Dg). 



457 times natural size. 

 Fig. 238. Part of section of segmenting egg, showing cell migrating from surface. July 31. 40 times 



natural size. 

 Fig. 239. Section of segmenting egg, showing yolk cell near center. July 31. 40 times natural size. 

 Fig. 240. Degenerating cells from same preparation as shown in fig. 237. y s, bodies resembling yolk 



spherules. 457 times natural size. 

 Fig. 241. Vesiculated masses of chromatin (Bg) undergoing degeneration in the yolk. From 



transverse section of early egg-embryo. July 18. 457 times natural size. 

 Fig. 242. Section of segmenting egg. Drawn July 31, 4 p. m. ; 34 cells present. 40 times natural size. 

 Fig. 243. Section of egg in late segmentation, showing formation of yolk cells and division of these 



in yolk. August 1. s c, cell at surface undergoing tangential division; y c, yolk cell in 



process of division. 40 times natural size. 

 Fig. 244. Surface view of egg in late segmentation of yolk. July 11. Fixed in Perenyi's fluid. 



About 50 times natural size. 



