162 METAMOEPHOSES OF MAN 



gives rise by gemmation to a series of new and 

 equally perfect individuals. In this instance the 

 scolex is directly converted into the proglottis, which 

 in its turn produces on all its sides an entirely new 

 generation of individuals which resemble itself. There 

 are, however, well-marked distinctions between these 

 two phases of development. 



Employing the same comparison adopted before, 

 we should say in this case, that the butterfly' s egg 

 produced, first, a caterpillar, which reached the final 

 condition ; then, from the butterfly which was thus 

 formed, others like the first were originated by bud- 

 ding, and the former was neither the father nor the 

 mother of the latter, but simply the parent. 



A somewhat more complex state of things takes 

 place among the aphides. 



The ovum which is deposited in autumn gives rise 

 to a scolex having nymphal characters ; and this 

 nymph produces no eggs during the summer, but 

 develops, instead, a number of genuine buds, which are 

 matured and organized in the interior of the body, 

 and not upon the external surface, as in the Hydra or 

 Aurelia. As soon, however, as the temperature of the 

 air becomes lower, the generative organs appear in 

 separate individuals, and we then find males and 

 females, or in other words true proglottides* 



* According to M. Heiden's published observations, an aphis 

 after having produced, agamically, and during the whole summer, 

 individuals like itself, can in the end of the season assume the 

 sexual characters. In other words, a scolex may be transformed 

 into a proglottis. The conclusions drawn from this fact regarded 

 as entirely new, are exaggerated. This transformation does not at 

 all alter the character of the phenomenon, especially when it is 

 viewed from our stand-point. Leydig, in a very valuable essay in 



