222 THE ZOOLOGIST. 



body was in the water, but the tip of the abdomen was never 

 submerged, even when all the rest of the body was covered. The 

 abdomen moved up and down with a rhythmic action, and 

 bubbles of air issued at more or less regular intervals from the 

 prothoracic spiracles. These air-bubbles were seen to form 

 gradually, to grow larger and larger, and finally to break away 

 from the spiracles ; about twenty per minute passed through the 

 spiracles. Air issued from the mesothoracic spiracles only when 

 the insect was violently agitated. From these observations it 

 seemed fairly obvious that the terminal abdominal spiracles were 

 inspiratory in function, the thoracic spiracles expiratory, and 

 that it was necessary, therefore, for the insect to have the tip of 

 the abdomen exposed to the air, but that it was a matter of in- 

 difference whether the expiratory spiracles were above water or 

 below it. In order to settle the question beyond all manner of 

 doubt, some specimens were fastened with cotton threads to 

 strips of cork ; half the number were fastened head downwards, 

 the other half head upwards. The cork- strips with the attached 

 insects were then immersed in tubes of water. In the case of 

 the reversed specimens the water covered the thorax and basal 

 segments of the abdomen, but the tip of the abdomen projected 

 above the water-level ; the other specimens had the abdomen in 

 the water, but the thorax exposed. The results in every case 

 proved the inspiratory and expiratory functions of the abdominal 

 and thoracic spiracles respectively. The reversed specimens 

 endured their constrained position for many hours (twenty-four 

 to forty-eight or more), and when released seemed little the worse 

 for their experience. On the other hand, the specimens with the 

 abdomen immersed in water died in less than twelve hours, some- 

 times in less than six. The structure of the thoracic spiracles 

 in Cockroaches is quite different from that of the abdominal 

 spiracles,* and a difference in function is only to be expected ; 

 nevertheless, when repeating these experiments with terrestrial 

 Cockroaches, such as Panesthia javanica, I was unable to demon- 

 strate satisfactorily the functional differences of their spiracles. 

 This failure may be accounted for — in part, at any rate — by the 

 fact that this species struggled long and violently when pinioned 

 to the cork-strips, and, as they are extremely muscular insects, 



* Miall and Denny, ' The Cockroach,' 1886, pp. 151-155, ff. 85-88. 



