xxxii INVEKTEBKATA 



FIG. I'AOK 



445. Sections tlirough eggs of Cynthia partita in order to illustrate the changes 



in form undergone by ectodermal and endodermal cells during the pro- 

 cess of gastrulation . ....... 616 



446. Illustrating the closure of the blastopore in the gastrula of Cynthia partita 617 



447. Optical sagittal section of gastrula of Cynthia partita . . . 618 



448. Dorsal view of an embryo of Cynthia partita after the closure of the 



blastopore in order to show the formation of the tail . . .618 



449. Transverse section through the middle of a gastrula of Cynthia partita . 619 



450. Longitudinal sagittal section of tadpole of Cynthia partita just before it 



escapes from the egg-membrane ...... 620 



451. Free-swimming tadpole of the simple Ascidian dona intestinalis, seen from 



the side ......... 621 



452. Anterior portion of free-swimming tadpole of the simple Ascidian Phallusia 



mammilata, seen from above ...... 621 



453. Illustrating the metamorphosis of the tadpole of Ciona intestinalis . 623 

 .454. Transverse sections through the brains of Ascidiau tadpoles in order to 



illustrate the development of the hypophysial tube and of the adult 

 ganglion ......... 624 



455. Longitudinal sagittal sections through the brain vesicles and hypophysial 



tubes of just fixed tadpoles of Ciona intestinalis- .... 625 



456. Transverse sections through the hinder part of the pharynx of a series of 



larvae and just fixed young of the simple Ascidian Ciona intestinalis 

 in order to illustrate the development of the heart pericardium and 

 epicardium ......... 627 



457. Illustrating the development of the genital organs in the simple Ascidian 



Molgula ampiilloides ....... 629 



458. Illustrating the result of the development of single blastomeres of the 



2-cell stage of the egg of Cynthia partita . . . . .631 



459. Section through the segmenting egg of Pyrosoma giyanteum at the stage 



of thirty-six blastomeres . . . . . . . 633 



460. Longitudinal sections through two embryos of Pyrosoma giyanteum in 



order to show the formation of organs in the Cyathozooid . . 633 



461. Two embryos of Pyrosoma gigantcum, viewed from the dorsal surface, in 



order to show the formation of organs in the Cyathozooid . . 634 



462. The embryo of Salpa fusiformis attached to the maternal placenta, seen 



from the side ........ 636 



463. Budding stolon of Perophora listeri showing the development of buds from 



the septum of the stolon ....... 638 



464. Stages in the development of the bud of Distaplia magnilarva . . 639 



465. Lateral view of old bud of Distaplia magnilarva .... 640 



466. Primordial colony of Pyrosoma giganteum consisting of four Ascidiozooids 



coiled round the degenerating Cyathozooid . . . .641 



467. Bud of a Botryllid almost completely developed and bearing two young 



buds, seen from the dorsal side ...... 642 



468. Four stages in the budding of a Diplosomid Ascidian . . . 643 



