624 



INVEKTEBEATA 



CHAP. 



dorsal wall of the hypophysial canal ; the visceral ganglion of the 

 larva, which formed the thick posterior wall of the brain-vesicle, 



FIG. 454. Transverse sections through the brains of Ascidian tadpoles to illustrate the 

 development of the hypophysial tube and of the adult ganglion. (After Willey.) 



A, B, sections through brain of a newly-hatched tadpole of Ciona inteslinalis : A, the more anterior 

 section, shows the pigmented otolith and the hypophysial canal running in the wall of the brain-vesicle ; 

 B, the more posterior section, shows the hypophysial canal opening into the brain-vesicle and the cup- 

 shaped support for the otolith. C, section through the brain of a just-fixed tadpole of Ciona intestinalis, 

 showing the degenerating larval brain and the hypophysial tube above it. D, section through the brain 

 of a young Ciona intestinalis, showing the adult ganglion as a new formation on the dorsal wall of the 

 hypophysial tube. E, F, sections through the brain of a tadpole of Clavelina lepadiformis : E, the 

 more anterior section, shows the brain-vesicle and the origin of the hypophysial tube and of the adult 

 ganglion from its wall ; F, the more posterior section, shows the cavities of the nerve tube and of the 

 hypophysial tube and the larva visceral ganglion, b.v, brain-vesicle ; gang.ad, rudiment of adult 

 ganglion ; gang.trisc, visceral ganglion ; hyp, hypophysial tube ; n.t, nerve tube ; oc, degenerating 

 remnant of the larval eye ; ot, otolith and its support. 



