400 Dr. J. Barrois on the 
There remains, however, a fact that I cannot explain, and 
which is shown by the series of figs. 6, 7, 8: while in the 
Entoprocta the frontal and tergal surfaces correspond to the 
posterior and anterior surfaces (that is, in the opposite direc- 
tion) of the larva, we see, on the other hand, that in the 
Ectoprocta the frontal and tergal surfaces correspond to the 
surfaces of the same name [in the larva], the frontal to the 
anterior, and the tergal to the posterior*. Figs. 6, 7, and 
8 will show this difference; it is an anomaly that I cannot 
explain, at least unless we assume that the pyriform organ 
(figs. 7, 8, ant.), hitherto regarded as indicating the anterior 
part in the morphological sense—?. e. corresponding to the 
subbuccal appendage (fig.6, ant.) of the larvee of Entoprocta— 
corresponds, on the contrary, to the posterior part, which cer- 
tainly seems at least doubtful, although, perhaps, its impossi- 
bility is not demonstrated. 
SIGNIFICATION OF THE METAMORPHOSIS. 
The Table of larval forms, already given, justifies us in re- 
garding fig. 1, the Entoproct larva, as representing the 
ancestral type of the entire group. To this, in fact, we have 
referred all the larvee, showing by what series of modifications, 
from this primitive form, were produced all the other types 
that we know; we have seen that the Hntoproct larva _pos- 
sessed the most complete organization of all, and that in all 
the other forms the primordial type has been altered. 
On the other hand, the study of the metamorphosis has 
shown us that there exist in all two great types of the trans- 
formation of the larva into the adult, types which present the 
same general phenomena, but in a more explicit manner in 
the former. Ina word, the development of the Entoprocta 
may be regarded as a dilated (palingenesic) and ancestral 
type of embryogeny, while that of various Kctoprocta, on the 
contrary, represents the condensed (cenogenesic) and derived 
form. 
employed to characterize the ventral surface. We avoid these ambigui- 
ties, and at the same time conform to all morphological and physiolo- 
gical requirements, by caliing the fixed surface ora/, and the free surface 
aborai, the latter being divided again into frontal (bearing the mouth) and 
tergal (corresponding to the anus), = : 
* If we suppose that in fig. 6 the digestive tube is turned through a 
semicircle, so that its anal and buccal apertures are directed downwards, 
we shall see that the mouth will come to be superposed upon the sub- 
buccal organ, ant. If we perform the same operation with figs. 7 and 8 
we shall see that it is the anus that comes to be superposed upon the 
peel mass, ant. It is in this that lies the want of concordance that 
cannot explain. 
