54 TRANSFORMATIONS OF INSECTS. 



produce fertile eggs without fecundation having occurred just 

 previously, and indeed this operation need not take place for 

 several generations. The egg-bearing by virgin females is termed 

 parthenogenesis, and will be noticed further on. 



In complete metamorphosis the larva is transformed into an 

 immobile chrysalis, pupa, or nymph, from which results a winged 

 imago, butterfly, moth, beetle, fly, or perfect insect. In the Crus- 

 tacea, the nauplius, zoea, and the perfect forms differ so much, 

 that although the quiet stage is not witnessed, the metamorphosis 

 almost deserves to be called something more than incomplete. 

 When the larva differs but slightly from the nymph (an active 

 chrysalis), which lives the same kind of life as and differs com- 

 paratively speaking little from the imago or perfect insect, the 

 metamorphosis is said to be incomplete. 



Hyper-metamorphosis will be noticed in considering the Sitaris 

 beetle, and it is only necessary to state here that a second larval 

 form springs from the pupa in that instance. 



A kind of hyper-metamorphosis occurs also in the creatures 

 which come from the nymphs of those spiders which respire by 

 means of tracheae — the mites and the water-mites — for these are 

 not perfect, and have to undergo an important skin-shedding, Avith 

 many internal alterations, before they are sufficiently organised to 

 reproduce their kind. 



Retrograde metamorphosis occurs in the true insects and in the 

 Crustacea. For instance, the female moths which come from the 

 chrysalides of the Vapourers and of some Psyches are less struc- 

 turally elaborate than their caterpillars ; and the barnacles, which 

 are immobile Crustacea, Avere once more highly organised, free, 

 swimming, and active creatures. 



The majority of the spiders, and, indeed, all those which do not 

 respire solely with the aid of tracheae, do not undergo metamor- 

 phosis, and the phenomenon is neither observed in the scorpions, 

 nor in the Myriapcda, or hundred-legs tribe, the Thysamira, or 

 skip-tails, or in the Anoplura, or lice. But the evolution of these 

 exceptional insects is accompanied by repeated sheddings of the 

 skin and mucous membranes ; and the moults often assume so 

 much importance as to approach metamorphoses. 



Some insects belonging to the same family, and even to the 



