SCIENTIFIC SURVEY OF TURNER'S LAKE 25 
some of which may perhaps be tactile; the spinose hump on the 
first abdominal segment (pl. 1, fig. 7) is directed forward and 
down and backed by a chitinized ridge. The photograph (pl. 2, 
fig. 1.) shows a small fragment of dried sponge with a larval 
case attached. 
This association is, perhaps, an example of dependent life in 
its incipiency ; for not only do certain individuals maintain their 
cases free from the growing sponge but one was noticed (pl. 2, 
fig. 2) which had started to decorate its case with small grains 
of sand and finished it off with spicules after having grown over 
half its normal length. If there is any advantage to be derived 
from the association in the way of food or shelter, it would seem 
to be a one-sided affair with the caddisfly on the long end of the 
bargain. When the case is stationary, the sponge probably 
reacts to it as it would toward any alien bit of rubbish and pro- 
ceeds to grow around and over it; when the larva continues 
active, the sponge tolerates it as a necessary evil along with 
other similar uninvited guests like the spongilla flies, Climacia 
and, Sisyra. But any temporary advantage is probably offset in 
the long run by the restrictions placed not only on the move- 
ments of individuals but by the limitations imposed by the 
distribution of the sponge itself. 
Frederic H. Krecker in the Ohio Journal of Science (1920, 20: 
355) reports the discovery of caddis-fly larvae (Rhyacophilidae) 
whose cases instead of being attached to sponges, were supporting 
living colonies and apparently acting as distributing agents. The 
larvae were dredged from Put-in-Bay, Lake Erie and appeared to 
have been actively crawling about in the bottom rubbish. In this 
case it would seem that the association might be of advantage to 
the sponge if it, as a normally sessile animal, is more rapidly or 
widely distributed. At any rate the condition is interesting in its 
oppositeness to that found in the sponge from Isle-au-Haut. 
