VI 



ANTENNATA—THE RESPIRATORY ORGANS 



479 



cases only a single pair of stigmata is left ; the tracheal system under- 

 goes corresponding modifications, the most important of which is the 

 connecting together of the originally separate bundles of tracheae by 

 means of transverse and longitudinal anastomoses. 



With reference to the scattered and irregular apertures of the trachess in the 

 Protrachcata, we must point out that the arrangement of the tracheal system in all 

 Antennata indicates a strictly segmental order of tracheal apertures in the racial form. 

 There is never more than one pair of trachefe in one segment in the Antennata. 



Myriapoda. 



The most primitive arrangement is found in the Diplopoda, where one pair of 

 stigmata and one pair of tracheal bundles occurs in each trunk segment. Each double 

 segment also has 2 pairs of stigmata and 2 pairs of tracheal bundles. The separate 



Fig. 338.— Tracheal mass of a dorsal plate of Scutigera coleoptera. A, from above ; B, in 

 transverse section through the inter-segraental fold of the dorsal plate ; diagrammatic (after Haass). 

 The tracheffi, which enter the air cavity (ca) from both sides, are marked white, vs, Anterior ; lis, 

 posterior stomatic aperture ; 05 (A) and se (B), outer ; ms (A) and si (B), inner stoniatic slit. 



tracheal bundles are not connected by anastomoses. Each stigma leads into a 

 tracheal sac, whose base is produced in the form of pointed horns, into which the 

 numerous but unbranched trachefe enter. Branched tracheae seem to occur only in 

 the Glomeridm. 



The tracheal system of the Chilopoda is seen to be a secondaiy development from 

 the fact that the traehete branch profusely, and that the trachea belonging to each 

 stigma anastomose with one another transversely and longitudinally. Only in 

 the Oeophilidce and Plutonium one pair of stigmata is retained on each leg-bearing 

 segment, except the first and last. In the species Lithohius and in the Scolopcndridce 

 (e.xcept Plutonium), beginning with the third trunk segment, a pair of stigmata is 

 found with considerable regularity on every second segment. The last leg-bearing 

 segment is here also without stigmata. In Scutigera and PTenicops the stigmata 



