xxx INVEKTEBKATA 



FIG. PAOK 



388. Diagrammatic transverse sections through the "Echinus-rudiment" of 



Echinoplutei larvae of Echinus esculentus, ranging in age from twenty-one 



to fifty days ......... 513 



389. Diagrammatic side-views of the larvae of an Asteroid, Echinoid, and 



Balanoglossid in order to show the comparability of the apical plate of 



an Asteroid with the larval brain of the other two types of larvae . 516 



390. Echinopluteus larva of Echinus esculentus, about fifty days old, just about 



to metamorphose, viewed from the left side .... 517 



391. Oral and aboral views of young sea-urchins immediately after the meta- 



morphosis ......... 519 



392. A series of diagrams showing the changes which the gut undergoes in 



Echinus esculentus after metamorphosis. The diagrams represent hori- 

 zontal sections through the young imago ..... 521 



393. Types of Lithium larva ....... 527 



394. The 32-cell stage in the segmentation of the egg of Synapta digitata, 



viewed from the side . . ... . . . 531 



395. The free-swimming gastrula of Synapta digitata .... 531 



396. Two young larvae of Synapta digitata, viewed from the side . . 532 



397. Three views of young Auricularia larvae of Synapta digitata, viewed from 



the dorsal surface, showing the division of the coelom . . . 534 



398. The fully-developed Auricularia larva of Synapta digitata, viewed from 



the ventral surface and from the side ..... 535 



399. Diagrams of the anterior aspect of metamorphosing larvae of Synapta digitata 



. in order to show the changes undergone by the longitudinal ciliated band 537 



400. Metamorphosing larva of Synapta digitata, viewed from the ventral aspect 538 



401. Pupa of Synapta digitata in two stages of development . . . 540 



402. Post-larval stage in the development of Oucumaria saxicola, viewed from 



the side . . . . . . . . .543 



403. Early stages in the embryonic development of Antedon rosacea . . 546 



404. External views of the embryo and larva of Antedmi rosacea showing the 



mutual relations of stomodaeum and ciliated bands . . . 548 



405. External views of larvae of Antedon rosacea at the time of hatching and 



after fixation in order to show the development of the calcareous ossicles 549 



406. Longitudinal sections through free-swimming larvae of Antedon rosacea . 550 



407. Fixed larva of Antedon rosacea, three and a half days after hatching, 



viewed from left side (decalcified) ...... 551 



408. Fixed larva of Antedon rosacea in which the vestibule is open but in which 



no trace of the arms have as yet appeared ..... 553 



409. Calyx of a larva of about the same age as that represented in Fig. 408, 



decalcified and cleared in order to show the internal structures . . 554 



410. Fixed larva of Antedon rosacea, viewed from the side, in order to show the 



origin of the arms ........ 555 



411. View of the calyx of a fixed larva of Antedon rosacea from the upper side 



in order to show the adhesion of the lobe of the hydrocoele to the arm 



and the first dichotomy of the arm ..... 556 



412. Map showing the mutual relations of the ossicles in the base of the calyx 



of a fixed larva of Antedon rosacea when the adult condition has been 

 nearly attained ........ 557 



413. The stalked larva and adult form of Antedon multispina . . . 559 



414. Diagrammatic reconstruction of the common ancestor of the phylum 



Echinodermata, and diagrams showing the modifications which the 

 descendants of this ancestor underwent in becoming the ancestors of the 

 Eleutherozoon and Pelmatozoon stocks ..... 563 



