middle hooks is much more massive than the lateral ones with a widened 

 and bifurcated upper part. The exterior offshoot of these hooks is some- 

 what sheered (truncated, nobis) at its free end-, whereas its interior is 

 more rounded and massive. The 2nd part of the middle hooks is con- 

 siderably longer than the first and has a strong point which then sharply 

 curves into a slightly curved handle which has almost a uniform width 

 along its entire length. The length of the lateral hooks is about 0. 02 mm 

 and the length of the 1st pair of the middle hooks is about 0. 027 - 0. 029 

 mm and that of the second- -0. 045 - 0. 055 mm. 



OMfMM 



Fig. 221. Diclybothrium armatum Leuckart, attaching armature of the 

 free -sw^i naming larva. 



"There is no doubt of the homology of the chitinous hooks of 

 the larva with those of the adult animals. The anterior 3 pairs of lateral 

 hooks correspond to the hooks of the suckers --clamps, the 4th pair to the 

 3rd pair of hooks of the narrowed part of the disc, the 5th pair corresponds 

 to the small hooks of the posterior end and in such a fashion is the only 

 one of them all not subjected to any noticeable change in sizes or form. 

 The Ist and 2nd pairs of the middle hooks of the larva correspond to 

 those of the narrowed part of the disc of the adult individual. It is curious 

 to note that the lateral hooks, strongly differing in form, and the 2nd pair 

 of middle hooks of the larvae acquire a very considerable sinailiarity during 

 further development. It is essential to bear this circumstance in mind 

 during the evaluation of the interrelations of the chitinous formations of 

 adult individuals for the formulation of phylogenetic links within the limits 

 of the group. " 



211 



