86 



THE YOUNG NATURALIST. 



[April, 



tracheae, which are membranous tubes, containing an elastic spiral 

 wound round and round. From the minutely microscopical character 

 of these air tubes or tracheae, it is only rational to anticipate some 

 considerable difficulty in tracing them, more especially in specimens 

 prepared in the usual manner for the microscope. I have found that 

 for the convenience of figuring these tracheae in their most intricate 

 ramifications, the upper wings of certain species of Orthoptera are 

 most suitable for the purpose, and Fig. i gives a highly magnified 



representation of a portion of the 

 tegminus or anterior wing oiLocusta 

 migratoria. From this it will be at 

 once seen that a very perfect and 

 highly complex system of tracheae 

 traverse the wings, the principal 



Fig. 1. 



Now if a specimen be taken 



branches being contained in the ner- 

 vures, the larger wings-rays often 

 possessing two main trunks running 

 parallel to each other, which again 

 send one or more branches of lesser 

 importance through the nervules 

 or inferior rays. 



from the upper wing of a locust, 

 carefully dried, and then immersed for a second in oil of cloves, and 

 quickly placed beneath a good J-inch objective, these tracheae will be 

 found for the greater part to be filled with air, and while the rest of 

 the wing is permeated and rendered perfectly transparent by the 

 action of the oil, the air tubes stand out as finely pencilled black lines. 

 On treating a specimen in this manner, it will be found that the ex- 

 ternal walls of the nervures are pierced in innumerable places by 

 filamentous and branched tracheae, spreading all over the adjacent 

 membrane, and which, under ordinary circumstances, are totally in- 

 visible. It is obvious that these secondary tracheae pass between the 

 two membranes comprising the wing, and are possibly attached to 

 one, or more likely to both, and I am further inclined to think that 

 the terminations of these tubes do not open into the external atmos- 

 phere, but have their extremities closed. I will not consider at 

 present the probable duties performed by the wing tracheae, as I shall 

 have occasion to again refer to them. 



Another most important consideration, and that will be found to 

 have considerable bearing upon the subject, is the minute structure 



