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The Relation of Mollusks to Fish in Oneida Lake 219 
CHAPTER V. MOLLUSKS AS PARASITES OF FISH. 
The intimate relation between the Naiades or fresh-water 
clams and fishes has but recently been given adequate scien- 
tific study. Ortmann, Lefevre, Curtis, Isely, Howard, 
Surber and others have placed the study of this interrelation 
‘upon a sound basis. The work accomplished at the United 
States Biological Laboratory at Fairport, lowa, has greatly 
increased our knowledge on the subject of the development of 
the fresh water clams and the studies carried on there have to 
a degree solved the problem of the rehabilitation of the 
depleted clam beds, so necessary as raw material for the mak- 
ing of pearl buttons, one of the principal industries of many 
cities and towns on the Mississippi River. The results 
obtained at Fairport illustrate forcibly the value of attacking 
these economic problems by scientific methods. 
The young of clams, known as glochidia, have long been 
recognized as parasites on the external parts of fishes, but 
their true relation to the fish, and to the mollusk, was not 
known for many years, and it is but recently that they have 
been studied in an analytical manner. To understand their 
true significance one must follow the development or meta- 
morphosis of a clam from the time the eggs are fertilized until 
the young clams are ready to begin an independent existence. 
Metamorphosis of Fresh-water Mussels. 
The metamorphosis or development of the fresh-water mus- 
sles or clams is quite as wonderful and as interesting as that 
of the butterfly or beetle and also quite as complicated. In 
the female clam one or both pairs of gills are modified to form 
marsupia or brood pouches into which the eggs are carried 
soon after being fertlized by the sperm which is taken in with 
the water through the inhalent or upper siphon. After a 
period of development the eggs become purse-shaped and the 
gills are swollen and distended by the mass of embryos pres- 
ent (Lefevre and Curtis, 1910, plates VI, VI, VIII). After 
the lapse of time, the length varying in different groups of 
