JAM S3 1903 



ON A CESTODE FROM CESTRACION. 399 



On a Cestode from Cestracion. 



By 



William A. Harwell, M.A., D.Sc, F.R.IS., 



Professor of Biology, University of Sydney. 



With Plates 22—24. 



General Features. 



The Cestode, the results of a study of wliicli are embodied 

 in the present paper, occurs, usually in abundance, in the large 

 intestine of the Port Jackson shark. It is one of these re- 

 markable forms to which attention appears to have been first 

 specially directed by P. J. van Beneden (1 and 2), in which 

 the proglottides are set free from the posterior end of the 

 strobila long- before full maturity has been reached, and only 

 attain a stage corresponding to that of the " ripe " proglot- 

 tides of a Taenia after having pursued an independent 

 existence for some considerable time. 



The sti'obila is actively locomotive, and appears to use the 

 suckers more in connection with progression than as organs 

 of permanent attachment. It is only 9 or 10 cm. long in the 

 preserved condition. There is an elongated neck-region Avith 

 a breadth, in the preserved specimens, of half a millimetre. 

 The four sessile bothridia (fig. 1) are somewhat spoon-shaped, 

 the anterior end being the narrower. The margin of the 

 bothridium is very prominent, finely crcnulate, and in the 

 living condition extremely extensile, so that the shape is 

 undergoing constant modification. In preserved specimens 



VOL. 46, rAlJT 3. — NEW SERIES. CB 



