NATURE OF EXCRETORY PROCESSES IN MARINE POLYZOA. 139 
swelling, doubtless formed from ectoderm, grows out towards 
the middle line, immediately beneath the ectocyst (fig. 10). 
The two swellings unite (figs. 11 and 12) and form a single 
rounded mass, which remains connected with the angles of the 
operculum by a tract of modified ectoderm, which soon dis- 
appears, on each side. The outer layer of the bud is colourless, 
and is formed from ordinary funicular tissue. 
In some cases the end of each bud-rudiment is considerably 
swollen before fusion takes place (fig. 11); in other cases no 
swelling appears until after fusion. In the former case the 
zocecium appears to possess two buds placed side by side. 
This mode of origin of the buds is no doubt the cause of an 
abnormality, frequently noticed, in which two polypide buds 
occurred side by side in the same zocwcium.! There was no 
doubt that in these cases each half of the polypide-bud had 
developed into a complete polypide, the normal fusion of the 
two halves having been, for some reason, prevented. Double 
polypides were observed in various stages of development, from 
the small ovoid stage, when the two halves should normally 
fuse, to the condition in which the tentacles of the two polypides 
are well developed. Each polypide then usually possessed a 
distinct tentacle-sheath, although in one case observed the two 
tentacle-sheaths fused distally, although separate at an early 
period of their development, when the double bud was first 
noticed. 
In a particular experiment, all the colonies which had been 
treated with indigo-carmine were observed 313 hours later to 
be remarkable for possessing a considerable number of zocecia 
with twin polypides; as many as six of these zocecia having 
been noticed in one small area of a colony. This probably 
indicated that the indigo-carmine abnormally present had acted 
1 This abnormality is recorded by Haddon (loc. cit., p. 520), as well as by 
Ostroumoff (‘ Arch. Slaves de Biol.,’ t. ii, 1886, p. 341). Ostroumoff found 
that the two alimentary canals were always united by their stomachs; which 
he explains by assuming that there were at first two buds, which later became 
united through the intermediation of a common “‘ brown body.” I am unable 
to say whether a union of this kind would have been effected later in the 
cases of twin polypides which I observed in their immature condition. 
