478 ANATOMICAL AND PATHOLOGICAL OBSERVATIONS. 



attached to it ; but that the other is quite free and almost 

 transparent. This transparent part was that originally 

 attached to the parent or germinal membrane ; and the shreds 

 are consequently the remains of the internal membrane of the 

 parent. Shortly before the young hydatid separates from the 

 germinal membrane of the parent, smaller cells are seen with- 

 in it, which increase in size along with it. These are another 

 generation of hydatids, and the fourth in the series I have 

 been describing. 



About this period in the process of development, there may 

 be seen in some forms of hydatids of the tertiary growth, a 

 dark irregular flat nucleated spot, which always occupies the 

 same place, immediately opposite that of attachment. Tliis 

 spot is visible only before the separation. I am inclined to 

 consider this spot as the first appearance of the pedicle, or 

 what is generally termed a head in the class. This species I 

 denominate Acephalocystis armatus. This appearance is merely 

 the nucleus or central cell, from which all the others are pro- 

 duced ; thus illustrating that the pedicles of Ctenurus and 

 Cysticercus are analogous to this nucleus, both being repro- 

 ductive organs ; — in the acephalocyst being a reproductive 

 organ only, in Caenurus and Cysticercus being chiefly a repro- 

 ductive organ with a slight adaptation for the purposes of 

 prehension. 



If the small cells which are seen in the tertiary hydatids 

 are the young, they must be the first of those which are after- 

 wards seen attached to the germinal membrane, for I have not 

 met with secondary hydatids enclosing separated young indi- 

 viduals. It is only after the hydatid has obtained a nidus, or 

 separate habitat of its own, that it begins to throw off its 

 young from the germinal membrane, and those only which 

 had been formed during the tertiary and secondary periods. 

 Thus, if the original hydatid is buried deep in the textures of 

 the infested being, or from other causes is prevented giving 



