SHELL GALLERY. 



fixes itself by papillae on the anterior end (Figs. 6, 7). Presently 

 the tail becomes absorbed, and the posterior end of the nerve-tube, 



Fig. 6. 



NOTOCHOBD 



Degeneration of Ascidiau Tadpole to form tlie adult. The black pieces represent 

 the rock or stone to which the Tadpole has fixed its head. 



ris. 7. 



MOUTH 



Very young Ascidian with only two gill-slits. 

 (Figs. 6, 7, from Laukester's ' Degeneration.') 



and the brain 'nith its eye and hearing organ, undergo atrophy, the 

 nerve-ganglion of the adult alone representing the cerebrospinal 

 axis of the larva. The branchial sac and intestines develop greatly, 



