VOL. XLVI.J PHILOSOPHICAL TRANSACTIONS. 5 



called hexipodes, creep up out of the water, and fix themselves on the shrubs 

 and rushes ; in this situation they continue but a few hours before their back 

 splits open ; and from this deformed case creeps out a beautiful fly, with shining 

 transparent wings : at its first appearance there is only what one may call the 

 rudiments of wings ; but it is a most entertaining sight to observe how they shoot 

 out, and expand themselves : thus, in less than an hour, they have attained 

 their complete dimensions. During all this operation the creatures are immove- 

 able, and so continue till their wings are dry ; and then they fly swiftly away, 

 roving about the sides of ponds and rivers, seeking their food, being insects of 

 prey, are very voracious, and, like the hawks among birds, are very swift of 

 flight, and nimbly secure their prey, which is mostly flies, and small green gras- 

 hoppers: they delight in sun-shine: in cloudy weather they are rarely to be seen; 

 but seek protection under the leaves and boughs of trees. 



Towards the end of May the female is ready to deposit her eggs. She then 

 seeks the warm quiet sides of ponds and water courses, continuing in a hovering 

 posture, dodging up and down in the water : in this action the male seizes her, 

 and with the end of his tail catches fast hold by the back of her head, and so 

 flies away with her. It is uncertain how long they continue in this position be- 

 fore the female bends the end of her body, so as to penetrate the part between 

 the belly and breast of the male. In this singular and surprising manner she is 

 impregnated ; she then repairs again to those still shallow waters, whose bottoms 

 are covered with moss, sticks, and weeds, which may be a security to the little 

 grubs. Here in a hovering posture she deposits her eggs in the water, which 

 immediately sink, and find a proper nidus in the aquatic moss, &c. The eggs 

 are soon hatched ; the young reptiles creep among the stones and weeds, &c. and 

 so continue water animals the gi-eatest part of the year, till the season comes 

 round for their appearance in that beautiful fly before mentioned, which is dif- 

 ferent from the European ; but their process agrees with the European, as it is 

 described by M. Reaumur. There is a great variety of this tribe of insects in 

 America as well as in Europe. 



Some Experiments on Respiration. By Albert Haller, Arckiater, Professor of 

 Physic at Gottingen, and F.R.S. Abstracted Jrom the Latin. N"494, p. 323. 

 The experiments related in this communication were made with a view to de- 

 termine 1 disputed points on the subject of respiration. 1 . Whether the inter- 

 nal intercostal muscles elevate the ribs, as Mayow asserts, or depress them, as 

 Galen, Boyle, and others maintain ? 2. Whether there is air, in an elastic state 

 between the pleura and lungs, or whether the lungs come into close contact with 

 the pleura ? 



Relatively to the first question, Professor H. describes the following experi- 



