DEVELOPMENT OF EMBRYO. 65 



inflated end, and upon the bottom of the cavity, the foundations 

 of the circlet of hooks are formed, and somewhat higher, on the 

 broadest part of the cavity, the sucking discs. The formation of 

 the hooks takes place, according to Wagener, in this way; a 

 broad, annular fringe of small points or hairs is formed, with 

 their bases seated upon the epidermoidal coat of the cavity. 

 Only the lower ones are permanent, and become converted 

 into an alternating double circlet of conical claws, like the horns 

 of antelopes, of which the inner become the larger and the 

 outer the smaller; the others fall off. As the point of insertion 

 of the hooks forms a narrow annular ridge, a limitation and 

 appendicular pouch is produced in the entire cavity of the cephalic 

 process ; this is the future rostellum. The points [of the hooks] 

 are slightly curved outwards, and directed forwards. As soon as 

 they have attained the size of the future unciui, their softness 

 and alterability under pressure disappear, their walls become 

 thickened by internal depositions in irregular stride, and at the 

 base the new parts are then formed, especially the radical pro- 

 cesses, the upper surface of which is a direct prolongation of the 

 claw. The internal cavity of the claws or uncini is shut off 

 by a peculiar formation, which is at first separated from the 

 rest of the mass of the hook, has usually a horseshoe-like form, 

 and represents the first foundation of the dental process. In the 

 year 1852 I figured a circlet of hooks in the ' Prager Viertel- 

 jahrschrift/ which is certainly to be regarded as a malformation. 

 If it be allowable to draw conclusions from these structures to 

 the normal ones, we might feel tempted to suppose the occurrence 

 in the formation of the shaft of a union of separate horny struc- 

 tures, but I believe, as a general rule, that in the formation of 

 the shaft nothing but a production of the hinder wall of the claw 

 takes place, and the attachment of peculiar structures to the 

 ready-formed parts of the hooks only takes place on the spot 

 where the dental process occurs. Moreover, no new formation 

 of the hooks takes place, and they are evidently of ecmal develop- 

 ment throughout. 



The mode of attachment of the hooks in the skin is not so 

 easily understood. Sacs are very common in the large-hooked 

 Tcenine ; this is easily perceived in preparations in which the hooks 

 have been removed by maceration, after they have been dried. 

 But this sac-formation is very imperfect in the Cysticerci, in com- 

 parison with the Tanice. 



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