

Physiology o/*IIaematopinus tenuirostris, Burnt. 107 



chea abuts. Immediately before this spot the passage between 

 the trachea and stigma is narrowest. Here there is an extremely 

 fine, somewhat curved rod, thickened at its upper extremity, 

 the closing lever of the stigma (fig. 3, e). The superior 

 thickened end of this rod is connected in the abdomen with the 

 lateral longitudinal muscles, in the thorax with the median 

 constrictor of the thorax (fig. 4, x) . Then, as soon as the 

 above-mentioned muscles contract, the lever is set in motion 

 and closes the trachea. When the contraction ceases it opens 

 again in consequence of its elasticity, and the little rod goes 

 back into its position of repose. 



The tracheae exhibit an exterior nucleated membrane, the 

 peritoneal envelope, and an interior chitinous spiral membrane. 

 They are divided into principal and subordinate stems, of 

 which the latter run out into the finest ramifications and go to 

 all the organs of the body. The connexion of the individual 

 stems by the tracheae is in this case a peculiar one, such as, so 

 far as I know, has hitherto been observed in no insect. From 

 the last abdominal stigma a tracheal stem runs inwards and 

 forwards (fig. 1, a). This is united with the corresponding 

 trachea of the opposite side by a transverse stem (b). At the 

 point of union the trachea bends suddenly towards the side of 

 the body (c). The trachea starting from the penultimate ab- 

 dominal stigma divides, after a short course, into two branches. 

 One of these (d) runs straight forwards, the other (k) inwards 

 to the viscera. Into the latter the tracheal stem coming from 

 the last stigma opens. This arrangement is repeated through 

 the whole of the abdomen, so that in each case the main stem 

 of the trachea of the posterior stigma joins the subordinate 

 stem of the trachea of the next anterior stigma. The tra- 

 chean branch starting from the first abdominal stigma alone 

 unites directly with the main stem from the thoracic stigma. 

 From the latter a branch goes to the anterior legs ; the main 

 stem itself passes into the head, and ramifies there. The tra- 

 chea which starts from the first abdominal stigma and passes 

 into the thorax emits a branch to each of the intermediate and 

 posterior legs. The tracheae serve, as Landois justly pointed 

 out, both to convey the oxygen of the air to the internal 

 organs of the animal's body, and also to fix the respective 

 organs in their places relatively to the chitinous skeleton and 

 to each other. 



In respiration we distinguish expiration and inspiration. 

 Expiration takes place as follows : — When the respiratory 

 muscles which we have found in the head, thorax, and abdo- 

 men contract, the body-cavity will be diminished, the interior 

 organs, and especially the cells of the adipose body, will press 



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