ILLUSTRATIONS xxvii 



FIG. I'A'.i: 



299. Sections through the developing eyes of young cuttle-fish to show the 



development of the lens ....... 366 



300. Transverse section of the eye of a nearly ripe embryo of Sepia ojficinalis . 367 



301. Early segmentation stages of the egg of Phascolosoma gouldii . . 373 



302. Later stage in the segmentation of the egg of Phascolosoma gouldii, viewed 



from the posterior aspect ....... 374 



303. Two views of the apical region of the segmenting egg of Phascolosoma 



vitlgare ......... 374 



304. Nearly sagittal section of an embryo of Phascolosoma vulgare at the stage 



when gastrulation is beginning ...... 375 



305. A Trochophore larva of Phascolosoma cii/i/n-r>\ a little more than thirty-six 



hours old ......... 377 



306. Nearly sagittal sections through metamorphosing Trochophore larvae 



of Phascolosoma ........ 378 



307. Young specimens of Phascolosoma gouldii after the metamorphosis . 379 



308. Lateral view of the Actinotrocha larva of Phoronis .... 381 



309. Diagrammatic frontal section of the Actinotrocha larva of Phoronis (sp l ) 



captured near Ceylon ....... 



310. Longitudinal horizontal section of the embryo of an Australian species of 



Phoronis ....... .382 



311. Three stages in the metamorphosis of the Actinotrocha larva of Phoronis, 



seen from the side ........ 384 



312. Early stages in the development of the egg of Mei)ibranipvra pilosa . 388 



313. The development of the larva of Mcmbi-anipora pilosa . . . 389 



314. Median sagittal section of the fully-grown Cyphonautes larva of Membrani- 



pora pilosa ......... 391 



315. Sections through fixed and metamorphosing larvae of Alcmbranipora 



pilosa ......... 393 



316. Two degenerate types of larvae of Ectoproct Polyzoa . . . 395 



317. Stages in the development of the bud of Bucjula avicularia . . 397 



318. Early stages in the development of the egg of Pcdicellina cchinata . 399 



319. Nearly sagittal section lying to the right of the median plane through the 



embryo of Pcdicellina cchinata . . . . 401 



320. Optical sagittal section of the free-swimming larva of Pcdicellina cchinata 402 



321. Median sagittal sections through two fixed and metamorphosing larvae of 



Pcdicellina cchinata ....... 404 



322. Optical sections of early embryos of Tcrcbratulina scptcntrionalis . . 408 



323. Later embryos of Tcrcbratulina septentrionalis seen from the side (in 



optical section) ....... 409 



324. Dorsal and ventral views of larva of Tcrcbratulina septentrionalis . . 410 



325. Lateral view of a larva of Tcrcbratulina scptcntrionalis . . 411 



326. Frontal and sagittal sections of the larva of Tcrcbratulina septentrionalis 412 



327. Two larvae of Tcrcbratulina septentrionalis just before and at the time of 



fixation ....... 413 



328. Two young Tcrcbratulina septentrionalis immediately after the meta- 



morphosis ........ 414 



329. Young Tcrcbratulina septentrionalis some little time after metamorphosis, 



viewed from the dorsal surface ..... 415 



330. Early stages in the segmentation of the egg of <.'!li<Jiint. /'usscofa . 419 



331. Further stages in the segmentation of the egg of I'uHiiliuii russeolu . 420 



332. Sixteen-cell stage in the segmentation of the egg of Cllitliim russi nfn . r_'l 



333. Two views of embryos of CaJlidina russcota showing the process of 



gastrulation . 422 



