The Origin and Transformation of Animals. 103 



meaning assigned by Sars to the term strobila, it will designate 

 every compound being which, proceeds from a scolex, and which 

 is destined to produce isolated individuals. Lastly, borrowing 

 from Dujardin an expression which he employs in a similar 

 sense, proglottis will designate the individuals springing from a 

 strobila, and which complete themselves by the acquisition of 

 reproductive organs, and thus close the cycle of development." 

 Between the primitive scolex and the strobila several generations 

 may, as we have seen, be intercalated, and in this case our 

 author calls the first scolex proto-scolex, the second deuto-scolex, 

 and so on, signifying first, second, etc. by Greek words. 



In the medusa, we saw that " each egg which it laid, pro- 

 duced not a single medusa, as a butterfly's egg yields a single 

 butterfly, but a great number of individuals. Secondly, 

 this reproduction took place in an indirect or mediate way ; for 

 between two generations of medusa, several generations of very 

 different creatures were produced by budding. To speak in a 

 still more general way, it is a case of multiple generation by the 

 aid of a single germ. It is that which I have endeavoured to 

 express by the word geneagenesis, which is applicable to every 

 method of reproduction that exhibits this characteristic feature.'" 

 The common polyp multiplies by buds, and also by eggs ; but 

 when it lays eggs it dies. Thus from the polyp egg comes a 

 single individual, a scolex, capable of producing others like 

 itself, which can bud in their turn and repeat the process, and 

 which end, like the original stem animal, in acquiring sexual 

 attributes. " It is as if there came from the egg of a butter- 

 fly, an animal having the appearance of a perfect insect, but 

 destitute of reproductive organs, although able to give rise by 

 budding to individuals like itself, and which, together with 

 itself, would ultimately acquire the attributes of a father and 

 mother." In such instances geneagenesis is reduced to its 

 simplest elements, each scolex transforms itself into a pro- 

 glottis, and the strobila stage does not appear. 



Among the ascidians, of which the Salpa may be taken as an 

 example, ' c the scolex transforms itself directly into a proglottis 

 which in its turn produces a whole generation of individuals 

 like itself. .... In this case, to follow our comparison, it is 

 as if the butterfly's egg produced a caterpillar which arrived at a 

 perfect state, and afterwards from the butterfly coming from the 

 primitive egg, other butterflies had sprung, of which it was nei- 

 ther the father nor the mother, but only the parent." With the 

 plant-lice we arrive at further complications. " The egg laid 

 in autumn engenders a scolex having the character of a nymph 

 or pupa. During the spring this nymph does not lay eggs, 

 but forms buds which arise and organize themselves in the in- 

 terior of its body, instead of making their appearance and 



