THE FRESH-WATER MUSSEL 



129 



Exercise 11. — Infection of Fish with Glochidia. 



(c) The glochidium of a particular species of mussel usually 

 parasitizes only a few species of fish or even a single species. How- 

 ever, attachment often occurs on species of fish that will not carry 

 the glochidia through their development. In such cases the glochidia 

 are sloughed off within a few days, but a demonstration of the attach- 

 ment to a host may be obtained from such material. 



poster/or ac/ofuctor . .. , -j. 



muec/& y ^p&r/carcf/a/ cavjty 



,digee>tlve g/anof g/och/of/a/ ^e// 



anu5 



anterior 

 ^ . odductor 



moi/t/i 



-gang//a 



3/p/?i 



gi/f 

 gr/oc/?/c//d/ hook 



J/'nes of growt/7 



foot 



Fig. 61.— Juvenile stages of fresh-water mussels. A, Sijmphynota, shortly 

 after leaving the fish. B, Anodonta, seven weeks after leaving fish. 



{A from G. Lefevre and W. C. Curtis. 1910, Bulletin V. S. Bureau Fisheries, vol. 30; 

 B, from K. Herbers, 1913, Zeitschrift fUr wissenschaftliche Zoologie, vol. 8.) 



(d) Take a considerable number of living glochidia in a finger bowl 

 of clean water and put two small fish into it. Watch how and where 

 the glochidia attach themselves. The water must be sufficiently agi- 

 tated, either by the activities of the fish or by stirring gently, to pre- 

 vent the glochidia from settling to the bottom. After five or ten 

 minutes, take one of the fish and put it into an aquarium. Kill the 

 other fish and remove its gills, fins, and tail without pressing on them. 

 Examine them in a watch glass with a microscope. How and where 

 are the glochidia attached? Draw one or more glochidia, attached to 

 a gill or fin, on such a scale as to make the larvae about 5 mm. in 

 diameter. Make an estimate of the number of glochidia on this one 

 fish; of the number produced by the single mussel. 



(e) The fish that was placed in the aquarium after infection should 

 be examined at succeeding laboratory periods, and the condition of the 

 glochidia with reference to the tissue of the fish determined. Fish 



