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DISTOMUM CIRRIGEBUM. 273 



On the Anatomy and Development of 

 Distomum cirrigerum, v. Baer. 



By 



Ernest W^arreii, D.Sc, 



Assistant Professor of Zoology, Universitj College, London. 



With Plates 24—26. 



Material. — In November, 1901^ my attention was drawn 

 by a student dissecting a male crayfish (Astacus fluvia- 

 tilis) to the condition of its muscles. The extensor muscles 

 behind the heart contained numerous rounded bodies of a 

 whitish translucent aspect, which varied in size from micro- 

 scopic dimensions to 1*5 mm. or more in diameter. On 

 examination these bodies proved to be cysts enclosing the 

 trematode Distomum cirrigerum, v, Baer. The living 

 animal could be seen revolving inside the cyst. 



Some of the extensor muscles were stripped off and fixed 

 in strong Flemming solution for about fifteen hours. The 

 remainder of the crayfish was placed in a large volume of 

 corrosive sublimate and 2 per cent, acetic acid for half an 

 hour. 



Adult forms and developing young were both found in the 

 crayfish ; the former occurred almost entirely in the extensor 

 muscles, while the latter were chiefly embedded in the thin 

 sheets of connective tissue over the muscles and around the 

 nerve-cord and the endophragmal skeleton of the thoracic 



VOL. 47, PAKT 3. — NEW SERIES. S 



