xxii INVEKTEBKATA 



FIG. l>A( " iK 



163. " Megalopa " larva of the Crab Pilumnus, dorsal view . . . 215 



164. Two views of first post-larval stage of Eupagurus bcrnhardi, corresponding 



to the Megalopa stage of Brachyura . . 216 



165. Two stages in the development of a Stomatopod larva . . .217 



166. Two later larvae of Stomatopoda . . .218 



167. Larva and adult female of Portunion maenadis . . .219 



168. Adult female of Portunion maenadis with appendages dissected out . 220 



169. Three stages in the segmentation of the egg of Agelena . . . 222 



170. Surface views of the developing egg of Agelena lalyrinthica, showing the 



primitive streak and the primitive cumulus 



171. Section through the primitive streak of Agelena to illustrate the forma- 



tion of the germ layers . . 224 



172. Two views of embryo of Agelena at the period of maximum extension of 



the ventral plate (i.e. before reversion has begun). The coelomic cavities 



are seen by transparence and are represented by lighter shading . 225 



173. Two sagittal sections through embryo of Agelena of different ages, but 



previous to reversion . . 226 



174. A portion of a sagittal section of Agelena lalyrinthica . 227 



175. Two views of embryos of Agelena undergoing reversion . . 227 



176. Transverse sections through the heart of Agelena lalyrinthica in two 



stages of development .... 



177. The embryo of Agelena when reversion is complete . 



178. Longitudinal section through part of the abdomen of Agelena lalyrinthica 



in order to show the origin of the genital organs . . 229 



179. Two sections through the developing stercoral pocket and ilalpighian tubes 



of Agelena lalyrinthica ....... 230 



180. Sagittal section through the hinder part of the abdomen of Agelena 



lalyrinthica to show the hinder part of the mid-gut developing in 

 connection with the stercoral pocket . . 231 



181. Longitudinal section through the abdominal appendages of an embryo of 



Agelena lalyrinthica in order to show the origin of the lung book . 231 



182. Surface views of the cut-off abdomen of three embryos of Agelena 



lulujrinthica of different ages in order to show the modifications under- 

 gone by the abdominal appendages ..... 232 



183. The condition of the brain in the embryo of Agelena after reversion has 



taken place ..... 233 



184. Sections through the developing eyes of Agelena . . . 234 



185. Two sagittal sections through embryos of the spider Thcridion maculatum 



in two succeeding stages of development ..... 234 



186. Horizontal section through abdomen of an advanced embryo of Agelena 



lalyrinthica in order to show the division of the yolk into lobes by septa 235 



187. Ventral view of an embryo of Limulus lonyispina, twenty-one days old . 237 



188. The Trilobite larva of Limulus .... .238 



189. Two transverse sections through the " germinal disc," or developing area, of 



the egg of the Scorpion Euscorpius carpathicus in two stages of development 239 



190. Ventral view of embryo of the Scorpion Euscorpius carpathicus showing 



segments and appendages ..... . 239 



191. Larva of Ascorhynchus minutus . . . 242 



192. Dorsal view (optical frontal section) of the embryo of Macrobiotus . 243 



193. Portion of a sagittal section through the developing egg of Doryphora 



(Lcptinutarsa] deccmlincata before the formation of the blastoderm . 246 



194. Surface view of the egg of Donacia crassipcs at the conclusion of blastoderm 



formation .... 247 



