STRUCTURE AND DEVELOPMENT OP LOXOSOMA. 313 
the attached oral face, as was previously the case. The ecto- 
derm of the free surface (aboral of larva) now becomes 
thickened (“ labial thickening’''), and subsequently invaginated 
to meet the part of the vestibule connected with the reversed 
gut. Into this portion of the vestibule the labial “ invagina- 
tion” opens, and forms the outer part of the permanent ves- 
tibule. The oral face of the larva thus becomes the aboral side 
of the adult, and vice versd, and the foot-gland of the adult 
Loxosoma is not homologous with the sucker of its larva. 
The sucker and the dorsal organ are both derived from the 
two primary layers of the embryo, but are simply larval sense 
organs of no morphological importance ; they disappear after 
the metamorphosis. 
By comparing these somewhat remarkable statements with 
figs. 13, 14, and 15 of PI. II of Barrois’s earlier memoir (13), 
it has appeared to me possible to suggest an explanation of the 
“ metamorphosis,” at least as probable as that of Barrois him- 
self. I would suggest (1) that the post-larval changes consist 
in a process of budding ; (2) that the surfaces of the adult are 
in every way homologous with the similar surfaces of the larva, 
so that the foot-gland of the former (Loxosoma) is the 
actual homologue of the sucker of the latter ; (3) that the 
cf labial thickening” of the fixed larva is the epiblastic thicken- 
ing which probably gives rise to the whole of the vestibular 
cavity of the first individual formed by budding ; (4) that the 
changes of the larval vestibule and alimentary tract described 
by Barrois consist in their atrophy, as in Loxosoma, de- 
scribed above, after the fixation, the hypoblastic cells of the 
alimentary tract probably giving rise to the stomach and 
other endodermic (?) tissues of the bud, as would seem to be 
the case according to Barrois’s own description; (5) that the 
sucker and the dorsal organ, like the other purely larval struc- 
tures, atrophy during the budding. 
If the post-larval changes are not to be regarded as a meta- 
morphosis, but as consisting in the production of a new indi- 
vidual, it is conceivable that the larva might just as well fix 
itself by its oral as by its aboral face, whereas, if it becomes 
