NATURAL HOSTS OF FRESH-WATER MUSSELS. 
Ill 
specimen taken at Fairport, September ii, had only 48 glochidia remaining, and two 
specimens out of a total of nine taken at New Boston, September 24, held 26 and 31, 
respectively, all the September material indicating much development. The same 
results are shown by some material from the upper Mississippi which Mr. W. B. Gorham 
secured while with the reclamation work of the steamer Curlew, when, on August 26, at 
La Crosse, Wis., he secured one fish holding 365 glochidia, well along in development, and 
another fish at Genoa, Wis., September 23, with development about completed. In the 
vicinity of Fairport ehena has been secured with well-developed embryos during the last 
week in May and during June, July, and August. This would indicate a comparatively 
rapid metamorphosis, which, in my opinion at least, does not much, if at all, exceed two 
months. 
A study of the material shows us that ebena undergoes no important increase in 
size of shell, and consequently no change in form, during metamorphosis. Figure ii 
shows a glochidium (side view) on the edge of a filament. By reference to the figure it 
will be noted that considerable development is indicated, the posterior adductor showing 
in place, and the foot considerably developed; this was taken August 13, and figure 12 
shows dorsal and ventral views of the same development. In the specimens taken 
September 24, shown by figure 13, the development is very clearly defined, the foot 
having reached what might be considered normal size, while the position of the anterior 
and posterior adductors and the protractor pedis is distinct; it is believed this young 
mussel would have left its host in a very short time. In the specimens taken June 18, 
1910, practically no development at all has occurred; the distal third of a gill filament of 
this infection is shown in figure 14. 
Particular attention is called to figures 12 and 13, where the cysts are shown off 
to one side of the young mussel, a characteristic feature of those which have attained 
sufficient development. It seems the young mussel has shifted its position, migrating 
as it were from its normal position in the cyst to a new one among the delicate filaments, 
disarranging them as indicated in the figure (12) on the right side; this movement is 
preliminary to its ultimate freedom. The young mussels are now lying on the surface 
of the filament beneath the mucous membrane covering it, while the epithelial cells 
forming the cyst proper remain unbroken, so that it has evidently pushed along beneath 
the membranaceous covering to its present position, the membrane having now adapted 
itself to the new conditions and formed, as it were, a new cyst which covers the entire 
filament and gives to the parasite much increased freedom of movement. This condition 
is more clearly shown by reference to figure 18, where the distinctly swollen area com- 
prising the new cyst is accentuated, though the magnification in this figure is much less 
than indicated in figures 12 or 13. 
In the more recent infections — that is, the young still in the glochidial stage, as shown 
by figure 14 — this remarkable condition does not exist, the development being such that 
the animal has no power of locomotion as yet. On the other hand, in specimens taken 
during September, there are many cysts having the appearance of these shown in figure 
13, simple, hollow, globular areas suggesting small tumors, unmistakably the former 
abode of some young mussel which has completed its metamorphosis and departed with- 
