214 
BULLETIN OF THE BUREAU OF FISHERIES. 
valves and secondly from the body proper, as indicated by Figure 4, which shows 
the definitive mantle cells springing from the regions of the gill buds. This brought 
about the isolation of the larval mantle to the two concentric areas at the center 
of each valve. 
With Lampsilis luteola, even with advanced cases, the author has never been 
able to find any trace of the appearance of the definitive mantle cells from other 
than the edges of the valves, with the result 
that the larval mantle cells as development 
progresses recede only from the edges of the 
valves, never from the body proper, to which 
they usually extend. 
It was often observed with luteola that 
there was a marked tendency for the larval 
mantle cells during the late stages of devel- 
opment to migrate toward the lower portions 
of the valves, such as is seen in Figure 7, 
which shows the bare areas on the valves 
just below the bases of the gill buds. This 
seemingly contradicts the reason usually ad- 
vanced with Anodonta for the destruction 
of the larval mantle, which is said to be 
brought about in a mechanical way through 
Fig. 7.— Encysted L. luteola shortly before end of para- ,, advancement of the definitive, man- 
sitism, showing piacentai-iike relationship existing be- t-J 16 advancement oi rue uennrave man 
tween larval mantle cells and involution of host tissue, tie Cells from all directions. LaUSe, then, 
int., intestine; l., liver cells; p. g., pedal ganglion; st., ma y h aV e been mistaken for effect, and 
statocyst; g. b., gill bud; l. m. c., larval mantle cdls; J . 
d. m. c., definitive mantle cells. The nuclei of red tll6 8,(1V£LI1C6 01 QGIlIlltl V6 IUdy 
blood cells are pictured in the involution of host tissue. mere ly be the result of a contraction 
of the larval mantle, so that the formation of the mushroom body is a natural 
process. 
MIDDLE PARASITIC STAGE. 
In the Anodontas this period is occupied with the destruction and absorption 
of the larval adductor muscle, in which the larval mantle is concerned, and with- 
out the aid of which this change could possibly not be accomplished. The studies 
of luteola were made from collected material of various stages, but none were at 
hand showing the atrophy of the larval adductor, so, unfortunately, the part played 
by the larval mantle cells in this process was not observed. It is hoped, however, 
to cover this stage with further work when the several developmental stages of 
luteola will be taken up more in detail. It is presumed, however, that the dis- 
integration and fusion of the muscle filaments occur as with Anodonta corpulenta, 
with ingestion by the individual cells of the larval mantle. 
FINAL PERIOD OF PARASITISM. 
During the last stage of development the foot of the larval mussel is largely 
developed and almost fills the mantle cavity. The definitive mantle has undergone 
