66 THE entomologist's record. 



articulated animals " (Ann. Sci. Nat. Zool. (7), xiv., pp. 404-456), M. H, 

 Killanes concludes that the sub-division of Arthropods into Branchiata 

 and Tracheata cannot be preserved, and suggests the following table, 

 as expressing better than any other, the affinities of the groups : — 



I Myrinpoda 



TBiantennata ... -<f IVripatus 



( Antennata < (_Insecta 



. ,T 1 J I Qi;adriantennata Crustacea 



Arthropoda < ^ ^ ^ t • i 



^ ] rn T . ( Limulus 



/ Chelicerata ... ... ... ■{ . ^ ^^ 



[ I Arachnida 



2. On the Sub-divisions of the Class Insecta. — The Class 

 Insecta is divided into Orders; the number of these is differently esti- 

 mated ])y different authors ; Packard {Entoiiiolo<ji/ for Beginners, 1889), 

 establishes sixteen. These Orders are generally arranged in three 

 gi'oujis, termed respectivel}^ A-metahola, Eemi-metahola, Kolo-metahola. 



A-metahola (without change). — The insects composing this grouj) 

 are such as undergo no distinct or regular metamorphoses. Each stage, 

 from the ovum to the perfect insect, resembles the previous one, except 

 that at eveiy change of skin the insect gets larger until maturity is 

 reached. The members of this group have no wings, and hence 

 are often called Aptera, although tlie Order is usually known in 

 scientitic works as Thysanura. Exam})les of this grouji are Sjjring-tails 

 (Poditra), Lepisma, A;c. 



Herni-metabola (half-change). — This grouj) contains those insects 

 which have their metamorphoses divided into three stages (or four, 

 reckoning the egg), but which do not differ much in a})pearance in the 

 several stages (excluding the egg). The stages are: — 1. The egg; 2. 

 The larva, which is smaller than the perfect insect and differs from it 

 in having no wings ; after several changes of skin the larva becomes : 

 3. The jDujoa ; this is active, has considerable powers of locomotion, and 

 possesses rudimentary wings. The larval and pupal conditions are often 

 now considered as constituting only a single stage, which is called the 

 " Nymph " stage. The pujja or (nymph) undergoes several ecdyses 

 (changes of skin) before the final stage is reached, which is : 4. The 

 mature imago ; characterised by the possession of wings, but otherwise 

 showing but little advance on the condition of the pupa. The Orders 

 included in this group are: — Dermaptera (Earwigs), Orthoptera 

 (Cockroach, Locust, Grassliopper, &c.), Blatyptera (Stone-flies, 

 Termites, etc.), Odonata (Dragon- flies), Bleotopteka (May-llies), 

 Thysanoptera (Thrips), IIemiptera (Bugs, Aphides, Coccida3). 



Holo-metabula (whole change). — The insects in this group have the 

 metamorphoses divided into four distinct stages, and present a very 

 different appearance at each stage. These stages are : — 1. Tlie ovum ; 

 2. The larva; this is sometimes jn-ovided with claspers as well as with three 

 pairs of true legs (which are usually ill-developed), and undergoes several 

 changes of skin ; o. The pu})a ; this is a quiescent form, incapable of 

 movement (except to the most limited extent), and incajjable of taking 

 nutriment, it undergoes no change of skin from the time that it is formed 

 until the imago emerges ; 4. The imago ; this differs exceedingl}^ from 

 both larva and i^upa ; the claspers of the former have disajjpeared, only 

 true legs are present ; the wings are usually remarkably well-de- 

 velojied. Neuroptera (Lace-wings, Ant-lion), Mecopjera (Scorpion- 



