ZOOLOGICAL 
ae S 
Natural size. Photo by R. C. Osburn. 
pora pilosa, described and known as Cyphon- 
autes. 
By means of this free-swimming larva the 
distribution of the species is obtained as in other 
sessile animals. The fresh-water Bryozoa, of 
which there are only a few species, of wide 
distribution, have asexual winter buds or gem- 
mules, known technically as statoblasts, in addi- 
tion to the sexual reproduction, but the marine 
forms do not develop statoblasts. A certain 
amount of distribution in the case of the marine 
species is also brought about by means of drift- 
ing seaweed and timbers, and species may oc- 
casionally be transferred over long distances on 
the bottoms of vessels. How many species thus 
transported can maintain themselves in their 
new surroundings is of course problematical, but 
probably not many of them survive when carried 
far out of their normal temperature. For ex- 
ample, the beautiful species, Membranipora 
tehuelcha, which encrusts the sargassum or 
gulf weed with a delicate white lace-work, is 
annually carried into the waters of southern 
New England, but has never been able to estab- 
lish itself on our coast. 
When the free-swimming larva reaches a cer- 
tain stage in its development it must become at- 
tached. If it happens to settle on mud or 
shifting sand it is lost, but if it is fortunate 
enough to come in contact with a pebble or 
shell, seaweed or submerged wood, or the hard 
SOCIETY 
BUGULA TURRITA, A PLUMOSE SPECIES. 
BULLETIN. 741 
structure of some other ani- 
mal, it attaches itself and 
becomes permanently locat- 
ed. It then undergoes a re- 
markable transformation or 
metamorphosis, in which all 
the organs of the larva de- 
generate and those of the 
adult develop. The ances- 
trula formed by this meta- 
morphosis is more simple in 
structure than the later in- 
dividuals of the colony, that 
is, it is not so highly spec- 
ialized. It is generally pre- 
sumed to represent an earlier 
stage in the evolution of 
the zooecium and is there- 
fore of interest in tracing 
phylogeny. 
The structure of the indi- 
vidual is fairly simple, but, 
considering its minute size 
it is rather complicated. 
There is a lophophore or 
peristome, either circular or horseshoe-shaped, 
surmounted by a crown of tentacles. These are 
covered with cilia, by the motion of which, the 
food, consisting of unicellular organisms, is di- 
rected to the mouth in the center of the lopho- 
phore. The iutestine is a simple U-shaped tube, 
differentiated into a gullet (in some cases pro- 
vided with a crushing organ or gizzard), a 
stomach and an intestine. The vent usually 
opens outside of the ring of tentacles (group 
Ectoprocta), but in one small group (Endo- 
procta), it opens inside of the tentacle ring. The 
whole lophophore with tentacles, mouth and 
anus, may be extended through the aperture of 
the test or body wall, or it may be withdrawn 
for protection. The nervous system consists of 
a single ganglion situated between the mouth 
and anus, but in spite of the apparent simplicity 
of the apparatus the animals are highly irritable 
and very rapid in their movements. 
Surrounding the intestinal tract is a spacious 
coelom or body cavity, and outside of this is the 
body wall. The thin living tissue of the body 
wall is protected by a chitinous or horny layer 
which is usually further strengthened by a de- 
posit of lime salts, forming often a remarkably 
strong, thick shell when fully calcified. This 
test is usually pitted, cancellated or ribbed in 
a manner peculiar to the species, and in some 
forms is perforated by one or more special 
pores. In some families a membranous area 
occupies more or less of the front wall of the 
