ANTEDON. 409 



the surface of the disc of specimens from various localities, 

 and other Crustacean parasites have been found sunk in 

 the tissues or inhabiting the alimentary canal. A pear- 

 shaped holotrichous Infusorian is frequently abundant in 

 the alimentary canal of specimens collected off the Isle of 

 Man and in the neighbourhood of Boscoff, and a 

 peritrichous form, HemisjJeiroj^sis antedonis infests the 

 surface of the body of Mediterranean specimens. 



Methods. 



Antedon may be killed rapidly and with the arms 

 fully extended by immersion in fresh water. Corrosive- 

 acetic mixture is a good fixative, but the writer's best 

 results were obtained by the use of corrosive-acetic 

 mixture 3 vols, and 10 per cent, solution of formalin 1 vol. 

 For sectioning, specimens which have died with the arms 

 fully extended laterally should be selected, so that 

 the primibrachials and proximal secundibrachials may 

 be as nearly as possible in the same plane as the 

 radials. After fixation, the specimens should be well 

 washed in several changes of 70 per cent, alcohol. 

 Decalcification may be effected by the addition of 3 per 

 cent, of strong nitric acid to 97 c.c. of 70 per cent, alcohol ; 

 and the specimens, especially if large, should remain in 

 this for at least twenty-four hours after bubbles of gas 

 have ceased to escape from them. All trace of the nitric 

 acid should then be removed by liberal washing in 70 per 

 cent, to 90 per cent, alcohol. For staining sections the 

 writer has used Heidenhain's iron hsem-alum method 

 with excellent results, and methyl-blue-eosin is also good. 



