6 THE FLATWORM AS AN ENEMY OF FLORIDA OYSTERS. 
perhaps death. During the early part of February, 1917, there was a 
decided fall in the temperature throughout the greater portion of the 
State and many orange trees, early gardens, and much vegetation 
in general were killed; also many small fishes, crabs, and oysters on 
the shallower reefs were destroyed. Following this extreme, the 
worms practically disappeared from the oyster beds, and relief was 
expressed by those engaged in the oyster industry. Just about this 
time local rains reduced somewhat the salinity of the water, which 
was also an unfavorable condition for the worms. 
Speaking of the turbellarian in New South Wales, Stead says: 
‘Judging by my present data, they appear to be most plentiful 
during dry weather (and particularly while mild or high tempera- 
tures prevail), when the water of our estuaries is of greater density.” 
Dry, warm weather appears to be the most favorable condition 
for this enemy. ‘The months of their greatest activity on the oyster 
bars are stated to be August and September, and if the weather con- 
tinues warm, October, November, and December may be included. 
The character of the oyster bottoms and the depth of water on 
the bars or reefs do not appear to have any direct influence on the 
depredations committed by the worms, since they were found active 
and damaging at all depths and on all kinds of bottoms, such as sand, 
firm mud, or shells. 
THE ATTACK AND RESULT. 
It is not known how the worm gains admission within the valves 
of the living oyster, and we were not fortunate enough, while exam- 
ining the beds, to obtain any data along this line. Itis probable that 
the soft, velvety creature may flatten itself into a very thin wafer- 
like form and slowly work its way between the partially opened 
valves without producing a reaction on the part of the oyster. Some 
oystermen, who have observed the habits of the parasite, are of the 
opinion that the entrance is made along the ventral margin or gill 
side, about halfway between the hinge and tips rather than at the 
tips themselves, since this is near the point where the worm is usually 
found. The first reaction of the mantle of an infected oyster takes 
place at this mid-portion of the shell. (See figs. 1 and 2.) It is 
possible that entrance is made during the larval or immature stage 
of the worm, at a time when admission could be more easily gained, 
and development completed within the oyster. 
* Regarding the method of attack the following remarks are made by 
tead: 
MetHop oF ATrack.—After gaining an entrance between the valves of the oyster, 
the wafer proceeds to wrap itself round the upper part of the oyster, as close to the 
great adductor muscle (which so powerfully keeps the two shells shut) as it can get. 
It then proceeds to pour out a great amount of thick, stringy, slimy mucus, which per- 
haps has the effect of partly digesting the body of the oyster, so as to prepare it for 
absorption by the wafer. Certainly in those which have come under my notice, the 
adductor muscle, usually the hardest part of the body of the oyster, is, after being 
attacked by the wafer, quite soft, although smelling quite fresh. 
One aspect of the case which is very puzzling is, as to how the worm gains entry 
between the shells of the oyster without the latter ‘“‘closing down’’ on it; as, if it did, 
the wafer would surely be nipped in two. 
The worm is usually found on the right side of the body of the 
oyster, near the heart, between the adductor muscle and the anterior 
