66 



HARDWICKE'S SCIENCE-GOSSIP. 



In March the isotherms run across England in a 

 North-Westerly direction. The mean average tem- 

 perature for the month at Devonport and Plymouth 

 is 45 . From Swansea to Dorchester it is 44°. On 

 a line drawn through Birkenhead, Warwick, Oxford, 

 London and Deal it is 43 , while at Lancaster, 

 Burnley, Sheffield, Lincoln and Norwich it is 42 . 



The average rainfall in March, for the greater part 

 of the South Coast, varies between one and two inches. 

 On the East Coast it is only one inch, while on the 

 South-West and West coast it varies between two 

 and three inches. 



PAPERS ON DRAGON-FLIES. 



The Metamorphoses of the Odonata. 



By W. Harcourt Bath, Author of "A Synopsis 

 of the British Odonata" etc. 



Chapter I. — Introduction. 



THERE is probably no group or section of 

 insects whose true position has given entomo- 

 logists more trouble to ascertain than the Odonata or 

 dragon-flies. 



Under the old Linnean system of classification, 

 insects are arranged according to some structural 

 resemblance which they bear to one another in 

 common, thus the character of the wings represents 

 the principal factor. This method, though it un- 

 doubtedly holds good in the majority of cases, fails 

 entirely to assign a proper arrangement of that 

 composite order known as the Neuroptera or nerve- 

 winged insects. 



Now the majority of the Neuroptera, it will be 

 admitted by all, resemble one another, so far as the 

 structure of their wings is concerned, but a criterion 

 of far greater importance is presented in the fact that 

 while two large sections of the order, namely, the 

 Planipennia (or true Neuroptera) and the Trichoptera 

 (or Caddis flies) possess complete or perfect metamor- 

 phoses, another large group, known as the Pseudo- 

 neuroptera (which includes the dragon-flies, day-flies, 

 stone-flies, and their allies), possesses incomplete or 

 imperfect metamorphoses. 



This vast distinction just pointed_out applied to our 

 present knowledge of the laws of evolution, ought to 

 be sufficient to separate the two first-mentioned 

 groups from the last one by a wide chasm, without 

 any reference whatever to structural affinities or 

 superficial resemblances. 



In order, however, to expel (as it were) the 

 Unionist party from its only stronghold, a very 

 powerful structural separatist doctrine has com- 

 paratively recently been promulgated by several 

 eminent entomologists (the Home Rule Party?) to 

 the effect that the formation of the mouth * in the 



Pseudo-neuroptera, together with the very general 

 presence of pointed styles or filaments at the ex- 

 tremity of the abdomen,* bears a remarkable ana- 

 logical resemblance to the Orthoptera. 



This, considered in conjunction with the much 

 more important fact, that the metamorphoses of the 

 Pseudo-neuroptera are similar to those of the 

 Orthoptera, effectually precludes the practicability of 

 the former ever again forming a natural alliance with 

 the Neuroptera. 



These considerations have even induced some 

 modern writers f to unite the Pseudo-neuroptera with 

 the Orthoptera— promoting the former group to the 

 rank of a sub-order. Still more recently other writers 

 have again reverted to the former system, but they 

 offer no substantial reasons for the lines which they 

 have adopted. + Thus the Pseudo-neuroptera have 

 been enacting the typical bat in the amusing fable 

 of the battle between the beasts and the birds. 



With the whole facts of the case now displayed 

 before us, it is not difficult for any one to determine 

 the true position of the Pseudo-neuroptera. They 

 may, without any hesitation, be proclaimed to be 

 connecting links between the Neuroptera and the 

 Orthoptera, for while they cannot be attached to 

 either group, by reason that they partake to a certain 

 extent of the structural characters of both, their 

 metamorphoses, which resemble those of the Orthop- 

 tera, point to their being more closely.connected with 

 the latter order. 



But, except in so far as is consistent with the object 

 in view, it is not my intention to give an exposition 

 of the biological position of the Odonata. I have 

 written this and the succeeding papers to give a brief 

 but clear outline of their metamorphoses, in order to 

 act as a stimulus for further observation and inves- 

 tigation on their behalf, for hitherto comparatively 

 very little has been recorded in connection with 

 dragon-flies. 



It will perhaps be necessary for me, in the first 

 instance, to give some of the most important struc- 

 tural characteristics by which the insects under our 

 consideration may be readily distinguished from 

 allied groups of the Pseudo-neuroptera. 



The imago possesses a large head, which is armed 

 with a powerful and complicated mouth. It has a 

 pair of very large compound eyes (which are con- 

 tiguous in some groups and remote in others), con- 

 sisting of a great number of lenses or facets. And 

 in addition there are three simple eyes, called Ocelli 

 or stemmata, which are situated on the crown of the 

 head, and arranged either in a straight line or in the 

 shape of a triangle. The antennre are awl-shaped. 



* See Brulle, M. Aug, "On the Mouth of Libellulida:," in 

 ' Annates de la Societe" Entomologique de France." Paris, 1854. 



* See Westwood, J. O., " An Introduction to the Modern 

 Classification of Insects," 2 vols., 8vo. London, 1840. Libellu- 



U t See Dales', Vs., « Cassell's Natural History," 6 vols., 

 8vo. London, 1882. Odonata, vol. vi. pp. 143-146. „ 



t SeeKirby, W. F., " Elementary lext Book of Entomology. 

 8vo. London, 1885. Odonat.., pp. £8-91. 



