56 SUMMARY OF CURRENT RESEARCHES RELATING TO 



appear late in larval life or only at metamorphosis. Clean-cut removal 

 of the antennae does not disturb dragonflies in the least. Smell seema 

 to be practically absent. Hearing is dubious, and is probably represented 

 by a sense of equilibration or poise. The larvte may have a chemical 

 sense. 



Tracheal gills are developed in the larvae of dragonflies in three 

 places : (1) in all Anisoptera, within the anterior portion of the rectum, 

 by specialization of the rectal epithelium and pads (forming the beautiful 

 branchial basket) ; (2) in most Zygoptera, on the two caudal cerci and 

 the appendix dorsalis ; and (3) on a few archaic Calopterygidse (which 

 have also caudal gills), on the sides of certain abdominal segments. 

 Besides these the rectal pads or folds of Zygopterid larvae probablv 

 function as blood-gills. The structure of the various types of gill is 

 described with great care. The spiracles of the larva are either closed 

 or only partly functional. 



"The dragonfly differs from all other insects in the fact that the 

 great muscles of the synthorax are directly connected with the wing- 

 bases by means of tendons. In all other insects the muscles by means 

 of which the action of the wings is controlled are not directly connected 

 with those organs, but are connected with the notum. . . . The 

 direct attachment to the wing- bases has been brought about by the 

 ■ development of special sclerites, derived from the notum, in the formation 

 of those bases." The fore and hind wings work quite independently. 

 There is only one true axillary or wing-pivot. 



The copulatory apparatus of the male dragonfly is one of the most 

 remarkable structures in the animal kingdom. It " is not homologous 

 with any known organ ; it is not derived from any pre-existing organ ; 

 and its origin, therefore, is as complete a mystery as it well could be." 

 A careful description is given. 



The egg, when laid, consists of the nucleus, the formative proto- 

 plasm in the yolk, the periplasm around the yolk, the yolk, the vitelline 

 membrane, the chorion with one micropyle, and some gelatinous matter. 

 The embryonic development is described. 



Out of the egg comes a " pronymph " enveloped in a cuticular 

 pronymphal sheath. It swells very rapidly and moults, liberating the 

 free-swimming larva. There are eleven to fifteen instars, each with an 

 ecdysis. The larva may reach maturity in a year, or not for five years.. 

 The " mask " is a transformation of the second maxillte. The changes- 

 during larval life include the appearance of ocelU, the increase in the 

 number of elements in the compound eye, the increase in the number of 

 joints in the antennae from three to seven, the development of wings, 

 the correlated changes in the thorax, the increase in the number of 

 Malpighian tubes, and so on. The final metamorphosis is described,, 

 with some reference to the peculiarities in Fetalura gigantea. 



After _ discussing the classification (429 genera, 2457 species), the 

 geographical distribution, the fossil forms, the author concludes his fine 

 monograph with a very interesting paper on bionomics, an account of 

 British species, and practical advice as to coJlecting and preserving. , 



