E. B. Wilson—Polycheetous Annelides. 291 
The latter, figure 2, F, is a median unpaired structure on 
the ventral surface of the body between the mouth and the anus. 
In the pulmonate and in many other gasteropod embryos a 
large sinus space, C, separates the integument of the foot from 
the.endoderm and its derivatives; the integument is rhythmi- 
cally pulsatile, and the sinus space has the function of a circu- 
latory organ. 
The only unpaired structure on the median line of the ven- 
tral surface of the body of the cephalopod embryo is the large 
food yolk, figure 1, Y, and in this, if any where, we must find 
the homologue of the gasteropod foot. 
In the cephalopod a sinus space, C, separates the food yolk 
from the layer of integument, F, which surrounds it, and this 
wall of integument is rhythmically contractile, like the foot of 
the pulmonate embryo, and I think we must conclude that the 
cephalopod foot, as a locomotor organ, has been suppressed 
by the great development of a food yolk at the point where it 
should be found. 
The arms of the squid make their appearance as little eleva- 
tions, A, A, A, arranged in pairs around the neck or constric- 
tion which separates the food yolk from the body proper. 
As they are, at first, ventral to the mouth, and as a true 
velum is present, we cannot accept Grenachers’ view that they 
represent this structure. s they are paired structures we 
cannot agree with Huxley in regarding them as the representa- 
tive of the foot, although they are, perhaps, to be regarded as 
paired outgrowths from the foot-region. 
e siphon originates as two pairs of folds, S and 8’, of the 
integument of the lateral walls of the body, and if we follow 
Huxley in regarding these four folds as homologous with the 
epipodial folds of a gasteropod, we must regard the arms as 
structures which have been independently acquired. 
on the other hand we regard the arms as modified epipo- 
dial folds we must consider the four siphon folds to be inde- 
pendently acquired structures, and in the absence of any test 
nothing seems to be gained by the uncertain homology of 
either the arms or the siphon with any part of the body of a 
typical gasteropod. 
Beaufort, N. C., July 5th, 1880. 
No. IL.—Notes on the Early Stages of some Polychatous Annelides ; 
by E. B. WILson. 
__In view of the morphological interest of the marine annel- 
ides as the most highly specialized forms among the “ Vermes,” 
and the scarcity of detailed accounts of their early stages of 
development, the following preliminary abstract of studies 
