DR. E. B. WILSON ON THE DEVELOPMENT OF RENILLA. 785 
178°) stretching between the wall of the cesophagus and the lateral wall of the bud. 
These are the septa. They have the same structure as in the young primary polyp, 
consisting of two layers of entoderm cells separated by a delicate supporting lamella 
which joins that of the body-wall. As the septa are formed the outer wall of the 
bud becomes divided into eight lobes (fig. 184%) which correspond with the eight 
chambers of the body. As the bud grows outwards (ef: fig. 205,) the septa grows 
inwards (7.e., downwards toward the axial polyp) so that their lower extremities remain 
at about the level of the body-wall of the primary polyp. 
The septa when first formed stand at nearly equal intervals from each other, though 
those on the dorsal side are often a little more crowded than the others. As the bud 
develops farther the septa assume a definite arrangement as shown in fig. 184%. The 
ventral pair approach more closely so that the ventral chamber, which is opposite one 
end of the elongated mouth, becomes distinctly narrower than the two adjoining 
ventro-lateral chambers. As shown by the later development, the narrow ventral 
chamber is homologous with the ventral chamber of the axial polyp and we are thus 
enabled to determine the orientation of the young polyp. We find that the dorso- 
ventral axis of the bud has a constant position with reference to the primary polyp, 
which is shown in fig. 184°; a—p represents the long axis of the primary polyp, and 
d-v the dorso-ventral axis of the bud. The latter cuts the former nearly at a 
right angle, but is always inclined slightly forwards (a represents the anterior 
extremity of the axial polyp). 
I will add a brief account of the habits of the young colony at this stage. 
If the creature be left to itself it gradually comes to a state of rest, burying the 
peduncle in the sand. The body always assumes nearly the same position, the dorsal 
side (as determined by the interior structure) being held upwards and the buds extend- 
ing horizontally on either side. The anterior part of the main polyp, with its crown 
of tentacles, is directed obliquely upwards and forwards. This position is maintained 
throughout all the following stages, and this is, I believe, a fact of the greatest import- 
ance which stands in causal connexion with the bilateral symmetry of the organism. 
The tentacles of the axial polyp may at this stage be entirely retracted into the 
anterior part of the body. This is effected by the invagination of the oral end of the 
body, the tentacles being at the same time strongly contracted. When fully 
expanded they are held nearly horizontally with the outer portion curving gently 
backwards. When the polyp is hungry the tentacles are moved actively back and 
forth, somewhat after the fashion of a Synapta, but without regularity. If supplied 
with food, such as Gasteropod veligers, the tentacles close eagerly upon it, and 
it is held for some time closely clasped by them. They are then taken into the 
cesophagus and passed in a bolus down to its lower portion where they remain for 
some time, the lower opening of the cesophagus remaining tightly closed. The 
