282 Destructive Nature of the Boring Sponge. [ May, 
in closing had torn a part of it loose, which had been repaired by 
the deposition of a brown horny substance. Evidence of the 
presence of the boring sponge may very frequently be noticed in 
shells of oysters brought to the markets, though it often appears 
as if the parasite had left its work incomplete, being killed on its 
host. I find that Schmidt has also’noted this, and that the boring 
operations of the sponge usually seem to stop in the case of 
living mollusks, at the nacreous layer. 
Dr. Leidy (l. c.) gives a lucid account of the living sponge as 
found in Ostrea virginiana and Venus mercenaria, He says, “ This 
boring sponge forms an extensive system of galleries between the 
outer and inner layers of the shells, protrudes through the perfora- 
tions of the latter tubular processes, from one to two lines long, 
and one-half to three-fourths of a line wide. The tubes are of 
two kinds, the most numerous being cylindrical and expanded at 
the orifice in a corolla form, with their margin thin, translucent, 
entire, veined with more opaque lines, and with the throat brist- 
ling with siliceous spicule. The second kind of tubes are com- 
paratively few, about as one is to thirty of the other, and are 
shorter, wider, not expanded at the orifice, and the throat unob- 
structed with spicule. Some of the second variety of tubes are 
constituted of a confluent pair, the throat of which bifurcates at 
bottom. Both kinds of the tubes are very slightly contractile, 
and under irritation may gradually assume the appearance of 
superficial wart-like eminences within the perforations of the 
shell occupied by the sponge. Water obtains access to the inte- 
rior of the latter through the more numerous tubes, and is 
expelled in quite active currents from the wider tubes.” 
A point of considerable interest in this connection is Mr. W. J. 
Sollas’! discovery of the existence of membranous and spiculifer- 
ous diaphragms in some English species of these sponges. These 
diaphragms are composed of sarcode in which, in some instances, 
very short club-shaped spicules are imbedded, pretty densely 
packed together, with their opposite extremities lying at opposite 
surfaces of the diaphragm. In some cases the diaphragms are 
perforate, forming an annular band inside ‘the canal and attached 
by an edge, the other edge being constricted somewhat, so that 
the bands sometimes have the form of hollow truncated cones. 
In other instances these partitions are membranous films contain- 
1 Am. Mag. Nat. Hist., 5th Series, Vol. 1, No. 1, 1878, p. 54. 
