324 Mr. C. H. Goodman on the Respiration of Insects. 



inspiration the effect would be to drive the air up the trachea, 

 though it is probably owing to what is known as the diffusion of 

 gases that the supply is renewed in the finer extremities. It is 

 in the thorax that the larger spiracles occur, and it is through 

 them that the buzzing sound is chiefly produced. Small 

 chambers have been found in some insects behind the spiracle 

 at the entrance of the trachea, and it seems probable that the 

 vibration of certain chitinous processes in this locality have much 

 to do with it. The muscles of the wings are attached to the 

 thorax, and not to the wings themselves ; consequently, as the 

 capacity of the thorax is altered with every flap of the wings, 

 respiration is effected at the same time, the more rapid the flight 

 the quicker the breathing. 



We have now lastly to examine those methods by which 

 respiration is carried on where no spiracles exist. The number 

 of insects thus provided is comparatively few, and they are all 

 aquatic larvfe breathing by means of branchiie, although they 

 are not so highly developed as those with spiracles. I have left 

 them till the last for the clearer understanding of the subject. I 

 must, however, mention that there are some few insects known 

 to science which possess both branchiae and spiracles at the same 

 time, and I regret I have been unable to get an illustration for 

 you, though one at least is a British insect. Such forms are 

 particularly interesting to the evolutionist as examples of an 

 intermediate transitional stage. 



We will take that of Acjrion first, as being the most common 

 and almost always to be found. The tail is seen to be composed 

 of three leaf-like flaps attached to the last segment. The 

 microscope shows them to be ramified by tracheae, and it is by 

 asmotic action through their thiii tissue that the air is supplied 

 to the trachefe. Another common form is the little white bunch 

 of filaments seen on either side of the head in Chirononuts 

 jilunwsits, the cast-skins of which are often found floating on 

 ponds, and make beautiful opaque objects with the side reflector. 

 Each slender filament carries its own trachea. 



The Ephemeridfe furnish many interesting species in their 

 larval condition. One of the commonest (a species of Boetis) 

 has seven pairs of oval laminate gills, articulated at the end to 

 the hinder edge of each segment of the abdomen. It is abun- 

 dant in the Hogsmill Eiver at Ewell. Ephemera imlgata has six 

 pairs of bifurcate plumose gills. I have found their cast-skins 

 by thousands in the Basingstoke Canal in May. Another species 

 (probably Chvon dipteriiin) has its branchife of a fan-shape, double, 

 a smaller in front of a larger, and on the dorsal margin of the 

 abdomen. In this species, which I have taken at Epsom, the 

 tracheae were most distinct. In other instances the specimens 

 may have been younger, as they frequently are not developed 



