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Transactions of the Society . 
through the sac walls, in which case it is difficult to understand 
how the capillary trachese can be employed at any period of the 
larval existence. 
Fig. 32. — Tubes attached to valve ends of pair of posterior sacs, with 
detail showing cells and granular bodies disposed in between them. 
The tracheal tubes have been torn off the free end during dissection. 
An alternative hypothesis has been advanced [(Frankenberg) 
that the entire gas is drawn from the blood and passes into the 
sacs. The necessary expansion of the bladder wall to take up the 
gas is due to the wall having strongly hygroscopic properties. 
