SIGNIFICANCE OF LARVAL MANTLE OF FRESH- WATER MUSSELS. 
213 
luteola, however, there is no indication of any vacuolated nature that in the Anodon- 
tas represents an excessive hypertrophy of the structure. This first increase in 
size probably represents the transformation from a secretory cell to a nonsecretory 
ingestive cell, characterized by a protoplasm of a more watery consistency. There 
is not the rapid change in the appearance of the nuclei, which retain their dark 
compactness into an advanced stage, so that they are not as readily distinguished 
from ingested cell nuclei as is true with the Anodontas. The nucleoli are only 
rarely prominent at this time. 
These individual mantle cells, although separated at their free ends, are closely 
attached along their bases and undoubtedly have the same function as has the 
larval mantle of Anodonta, although with the latter the transmission of food is 
apparently of a simpler nature in view of its homogeneity. With the individual 
cells of luteola there must occur a transfusion from 
cell to cell, so that the matter of functioning 
presents this slight difference. 
At the end of the third day we have with 
luteola a stage represented by Figure 6, in which 
all cellular detritus has been utilized, the indi- 
vidual mantle cells standing out clear and dis 
tinct, which is a contrast at this stage with the 
agglutinated appearance of the Anodontas, in 
which the boundaries of the mantle are so poorly 
indicated. 
There is a similarity at this time in both 
corpulenta and luteola in connection with the 
development of the lateral pits, Which form Fig. 6.— Encysted glochidium of L. luteola three 
inward involutions, later giving rise to the gill 
buds and having the effect of pushing the mantle 
cells from the region of the body proper. As a 
result of confining the mantle cells to a smaller 
area they become more elongate, which condition 
is retained from this time to the end of parasitism, 
stages is there any sign of degeneration. 
days after encystment. The epithelium of 
the fold of host tissue has become completely 
disintegrated, leaving only the connective tis- 
sue (e. t.) in which are visible the red blood 
cells ( b . c.). All the ingested food of the man- 
tle cells has been utilized, no nuclei or cell 
detritus remaining. 
At no time during subsequent 
ABSENCE OF “MUSHROOM BODY.” 
In the Anodontas the evidence of degeneration supposedly lies in the trans- 
formation of the mantle into the mushroom body, which marks the end of the 
intracellular nutritional function of the larval mantle, after which nutrition is 
taken care of by the definitive mantle. Thus, in the absence of any mantle trans- 
formation in Lampsilis luteola, there is this important difference, that the larval 
mantle functions as a nutritional organ during its whole existence, showing a more 
adaptive relationship than does that of the hooked glochidial type. 
FORMATION OF DEFINITIVE MANTLE. 
Herbers has emphasized the fact that the Anodontas are characterized by the 
formation of the definitive mantle from two directions, first from the edges of the 
