122 A NATURALIST IN BORNEO 



This, indeed, is the way in which the creature 

 breathes ; air is taken in at the abdominal spiracles, 

 and, passing through the tracheae, emerges at the 

 thoracic spiracles, the exchange of air being as rapid 

 as in warm-blooded vertebrates. 



The structure of the thoracic spiracles of the Water- 

 Cockroach, of which there are two pairs, is different 

 from that of the abdominal, of which there are eight. 

 The former are slits opening between a pair of thick, 

 lip-like valves that shut and open by means of muscles 

 attached to them. If a living Cockroach be held in 

 the fingers and the thoracic spiracles be examined with 

 a lens, it will be seen that the lips open and close 

 with rhythmic regularity. The abdominal spiracles, on 

 the other hand, are circular or oval openings, which 

 remain open permanently, but they have an internal 

 valvular arrangement which cuts off communication 

 with the tracheae with which each is connected. The 

 spiracles of the terminal pair in the Water-Cockroach are 

 situated each at the base of a short tube projecting 

 from the last segment but one, and it is these which 

 are thrust above the surface of the water, and through 

 which the animal draws in its air-supply. 



In order to make sure that it was the terminal 

 abdominal spiracles which were inspiratory and inspi- 

 ratory only in function, and the thoracic spiracles 

 expiratory only in function, I submitted some Cock- 

 roaches to experiment. They were pinioned back 

 downwards by cotton threads to strips of cork, placed 

 in glass tubes containing water, some being placed 

 with the attached Cockroach upside down, others with 

 the Cockroach right side up. In the former the sur- 

 face-level of the water was regulated so as to reach 



