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 Cras- 
tacea, the nauplius, zoéa, 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 Sizarzs 
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 trachea—the mites and the water-mites—for these are 
not perfect, and have to undergo an important skin-shedding, with 
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 Crwstacea, were 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 trachee, do not undergo metamor- 
phosis, and the phenomenon is neither observed in the scorpions, 
nor in the J/yriapeda, or hundred-legs tribe, the 7ysanura, or 
skip-tails, or in the Awoplura, 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 
