xxiv INVEKTEBBATA 



FTC. I'AOK 



220. Lateral views of the head of the larva of Dytiscus marcjinalis in three 



stages of development in order to show the gradual growth of the rudi- 

 ment of the compound eye .... 274 



221. Two stages in the development of the compound eye of Dytiscus marginalis 



as seen in longitudinal section .... 2/5 



222. A small portion of the adult compound eye of Dytiscus marginali as seen 



in longitudinal section ... 2/6 



223. Diagrams illustrating the metamorphosis of Musca vomitoria . . 277 



224. Two diagrams illustrating the metamorphosis of the head of Musca 



vomitoria . . . . .2/8 



225. Ventral view of the embryonic area in a developing egg of Scolopcndra 



cingulata ...... 



226. Development of Patella coerulca. Eight-cell stage showing the spindles 



preparatory to the formation of the 16-cell stage . . 293 



227. Two stages in the development of the upper hemisphere of the embryo of 



Patella coerulea, viewed from above . . . 294 



228. Stage in the development of the embryo of Patella coerulea, viewed from 



the vegetative pole of the egg, showing the first division of the third 

 quartette and the beginning of bilateral symmetry as seen in the 

 direction of the spindles in 3c and 3d 295 



229. Two stages in the gastrulation of Patella coerulea in optical longitudinal 



section ....... 296 



230. The "Ctenophore" stage in the development of Patella coerulca. Seen 



from above ...... 296 



231. View of the upper hemisphere of an embryo of Patella coerulea just before 



hatching ....... .297 



232. Lateral view of a late embryo of Patella coerulca showing the mode of 



completion of the pro to trochal girdle . . . 297 



233. Three diagrams of sagittal sections of the early larva of Patella coerulca 



in order to illustrate the shift of the blastopore and the formation of the 

 stomodaeum ..... 298 



234. Lateral view of young Trochophore larva of Patella coerulea . . 299 



235. Ventral views of two stages in the development of the Trochophore larva 



of Patella coerulea ........ 300 



236. Side view of a Veliger larva of Patella coerulca before torsion has taken place 301 



237. Side view of a Veliger larva of Patella coerulca after torsion has taken 



place .302 



238. Frontal section of a Veliger larva of Patella coerulca in order to show the 



mesodermic bands ..... . 303 



239. Frontal section through the pre-trochal region of an old Veliger larva of 



Patella coerulca ........ 303 



240. Two views of advanced stages of development of Acmaea virginca . . 304 



241. Three views of the just -metamorphosed Acmaea mrginca in order to 



show the formation of the adult shell and the loss of the larval shell . 305 



242. Two views of the young Haliotis tiolcrculata in order to show the forma- 



tion of the adult shell ..... .306 



243. Illustrating the results obtained by separating the blastomeres of the 



developing egg of Patella coerulca .... . 308 



244. Vertical section of the gastrula of Paludina vivipara . . 310 



245. Formation of the coelom in Paludina vivipara . . .311 



246. Optical frontal section of an embryo of Paludina vivipara a little older 



than those represented in Fig. 245 . . . 311 



247. Two stages in the formation of the pericardium of Paludina vivipara . 312 



