52 



expands. From this larva are produced other wingless 

 larvae, which are repetitions of the producer or parent; 

 these larvae in the Aphis remain disconnected from each 

 other, and do not combine to form a compound struc- 

 ture as in certain zoophytes ; they become detached like 

 the bulbels of the Marchantia or the lily, only they are 

 rather more advanced in individual development. But 

 under certain conditions a new and different series of 

 embryos forming male and female perfect insects are pro- 

 duced : these too become detached, and by their inherent 

 power of movement, through the possession of wings, they 

 carry the germs of a new generation to a distance from the 

 plants which their larval parents have devastated. The 

 whole of these phaenomena appear to me, as they did to 

 Bonnet, Reaumur, Dufour, and Morren, to constitute a 

 succession of generations, seven, nine, or it may be eleven. 

 But as all the larvae are like each other, they collectively re- 

 present with the perfect insects two generations, in respect 

 of form, and the generation of larviparous and the genera- 

 tion of oviparous Aphides may thus be said to alternate 

 with each other, in accordance with Steenstrup's general 

 expression of the fact. 



Now no physiologist has ever defined the series of virgin 

 larviparous Aphides, with the ultimately produced winged 

 males and oviparous females, as constituting a single gene- 

 ration, or the generation of the parts of one and the same 

 individual ; nor, if my comparison be true, have we better 

 grounds for so defining the succession of distinct animals 

 which have received the names of Hydra Tuba, Strobila, and 

 Medusa, or the succession of those which have been called 

 ciliated gemmules and planulae, digestive polypes, genera- 

 tive polypes, Tintinnabula or free medusiform polypes of 

 the Campanularia and Coryne ; or the successively deve- 

 loped cotyledons, leaves and flowers of a plant which are 

 combined by the stem into a seeming individual whole. 

 The analogy between the procreating larvae of the Aphis, 



