TiENIA EOHINOOOOCUS. 



267 



In the completely developed state, the echinococcus heads 

 exhibit somewhat variable characters as to size and form, the 

 latter differences being, for the most part, dependent upon their 

 degree of contraction and vitaUty. In the ftdly evolved condition 

 they vary from the -go' to the lio' i"! diameter, being usually about 

 the -js-\ They are solid throughout, and now exhibit a more or 

 less hourglass-Kke constriction at the centre of the body, which 

 divides the scolexinto an anterior part supporting the rostellum and 

 suckers, and a posterior part which has been erroneously compared 

 to the caudal vesicle of ordinary cysticerci. The rostellum supports 

 a double crown of hooks, but the disparity of the two series is 

 scarcely sufficiently marked to render their distinction readily 

 obvious. The hooks of the smaller row vary in size from i^ to 



Fig. 59. — Isolated and unfolded human Ecliinoooecus scolex, displaying the double crown of 

 hooks, cephalic suckers, calcareous corpuscles, and caudal pedicle (X 300 diam.)— Original. 



i^ of an inch, whilst those of the larger series are from -550" to 

 _^". In all instances, as shown by Leuckart, the root-processes are 

 incompletely developed, and, consequently, also vary much in thick- 

 ness. In some they exhibit pecuhar abnormalities, and, on 

 the whole, the echinococcus hooks may be said to be less perfectly 

 formed, in any case, than obtains in the corresponding scolecine or 

 cysticercal conditions of other tapeworms. As regards the other 

 structural features of these larvse, we find the suckers four in 

 number, and the general aspect of the body finely granulated ; 



