Embryogeny of the Bryozoa. 403 
Fig. 1. Larva of an Entoproct. The aboral surface is very large and 
forms the whole integument. The oral surface is small and 
sunk into a vestibule. The three internal organs are well de- 
veloped. 
Fig. 2. Larva of a Chilostome. The two surfaces are of nearly equal 
importance ; the chief part of the integument is formed by the 
circlet which represents the margin of the oral surface. The 
latter has lost the faculty of becoming retracted into a vestibule ; 
and the aboral surface is invaginated into a pallial cavity. In 
the internal organs we observe the reduction of a first internal 
organ (no. 2), which, instead of forming a complete intestine, 
has become reduced to a mass of vitelline globules. 
Fig. 3. Larva of a Ctenostome. Characters as in the preceding, but 
further presenting the reduction of a second internal organ, the 
sac (no. 3), which has become reduced to a little mass with no 
cavity. 
Fig. 4, Larva of a Cyclostome. The oral surface forms the whole of the 
integument of the larva, and is completely closed over the ab- 
oral surface. ‘The pallial cavity is thus transformed into a closed 
cavity. Of the internal organs the vitelline mass (2) has 
completely disappeared. 
Fig. 5, Larvaof a Lophopode. Characters as in the preceding, except that 
here the disappearance of the vitelline mass is associated with 
the complete disappearance of the sac. 
Fig. 6. Young cell of a Chilostome immediately after the metamorphosis. 
We see the construction of the polypide at the expense of the 
three parts 1, 2, 3. 
Fig. 7. Young cell of an Entoproct, showing the agreement with the 
preceding figure. In the polypide the white part represents 
what is derived from the organ no. 1 (hood), the grey part what 
is derived from the oral surface; the dotted part recalls the 
part taken sometimes by the residue of the opaque globules in 
the formation of the cecum of the stomach: the polypide thus 
shows that it is composed of three parts (1, 2, 3), which may be 
regarded as corresponding to the three internal organs (1, 2, 3) 
of the larve. 
Fig. 8. Young cell of a Ctenostome (Serialaria) represented in the same 
way. 
These Go Guzen, which alone may give a complete idea of the adult 
organism in the Ectoprocta, do not exist in nature, the invagi- 
nated vestibule always disappearing before the complete forma- 
tion of the polypide; but it is necessary to represent the two 
things simultaneously, in order to forma general idea of the 
animal. These two figures show us the position ef the polypide 
with relation to the invaginated vestibule. 
Figs. 6, 7, 8 show, further, the homologies of the different surfaces in the 
edunculate Bryozoa (fig. 6), the Bryozoa with flat cells (fig. 7, 
scharina), and the Bryozoa with tubular cells (fig. 8, Cellula- 
rina, Ctenostomata, &c.). The correspondence is complete in all 
respects except the orientation of the polypide. 
Fig. 9. Entoproct larva in the creeping state, to show the commencement 
of the immersion of the vestibule in the interior. 
Dies 
