CLASSIFICATION OF THE ANIMAL KINGDOM. 123 



forty-nine thousand six hundred eggs. The Aphides also are remarkable 

 for their fecundity, as "a single sexual intercourse is sufficient to impreg- 

 nate not only the female parent, but all her progeny down to the ninth 

 generation;" and one of these insects, it is calculated, might be the great 

 great grandmother of five thousand nine hundred and four millions of 

 young ones. 



With regard to the metamorphoses of insects, to which allusion has 

 been already made, Fabricius has divided them into five kinds — the 

 Coarctate, comprising all insects having a maggot larva without legs, and 

 its pupa encased in a small oval sheath; the Obtected, having a six-legged 

 caterpillar and a pupa, on which are indicated the future legs and wings 

 of the perfect insect; the Incomplete, having a maggot, without or with 

 imperfect legs, and a pupa having the form of the legs, antennae, and 

 wings perfectly distinct, though they are all still enclosed in cases; the 

 Semi-complete, having a larva like the imago, but without wings; and lastly, 

 the Complete, having a wingless imago, resembling the pupae. But there 

 are, says Professor Jones, "innumerable examples of metamorphoses which 

 will not conform to any of the above descriptions." The larvae or cater- 

 pillars differ considerably from the perfect insect in their external parts. 

 The viscera of the former are much more enlarged than those of the 

 latter, for obvious reasons. The caterpillars also possess the power of 

 secreting silk, which is subservient to the purposes of locomotion, and is 

 also used for protecting the defenceless pupa. The spinnaret, or orifice 

 through which the thread issues, is situated in the labium or under lip, 

 and is a simple nipple-shaped prominence. While growing, the skin of the 

 caterpillar is cast off at intervals, and when the moult takes place, not 

 only is the skin removed, but every part of the outward covering down 

 to the jaws and the cornea of the eyes goes with it. It is in the nervous 

 system, however, that the most interesting change takes place during the 

 insect-metamorphoses; and this beautifully illustrates the important principles 

 on which the arrangement of the animal kingdom by the distribution of 

 the nerves depends. In the larva;, the ganglia are numerous but small; 

 in the pupa state, the principal ganglion increases while others coalesce; 

 and when arrived at the imago or perfect state, we find a concentration 

 of the nervous centres adapted to the animal's increased necessities: and 

 the number of the small ganglia is still farther reduced, and encephalic 

 ganglion or brain still more highly developed. 



Having now considered briefly the anatomy and economy of insects, we 

 come to the next great class, the Arachnida — animals whose external 

 skeleton presents only two divisions — the cephalo-thorax and the abdomen; 

 they also differ from insects in the following ways — they have in their 

 perfect state eight instead of six legs, eyes invariably smooth and of a 



