V<1. IX. November, 1905. No. 6 



BIOLOGICAL BULLETIN 



THE DISTRIBUTION OF TRACHEA IN THE 

 NYMPH OF PLATHEMIS LYDIA. 



G. G. SCOTT. 



The Odonata are regarded as among the most highly organ- 

 ized of insects. In fossil dragon flies found in the Tertiary are 

 indications of high specialization. Dragon flies are especially 

 adapted to swift flight. For this purpose they are supplied with 

 broad wings and powerful muscles to work them. There is con- 

 sequently a great need for a plentiful supply of oxygen. This is 

 supplied to every tissue in all parts of the body by the tracheal 

 system. On this account a study of the tracheal system is of 

 interest and importance. 



The late Professor James I. Peck, of Williams College, sug- 

 gested to the writer in 1 898 that he make a study of the distri- 

 bution of tracheae in the nymph of a dragon fly found near Wil- 

 liamstown, Mass. It is from notes and drawings made at that 

 time that the present paper is written. The forms found were 

 identified by Professor James Needham as PlatJicmis trinmculata, 

 which name I am informed has since been changed to Plathetnis 

 lydia. Lubbock says that the larval tracheae of insects are more 

 generalized and represent more nearly the original type than 

 those of the adult. The results of this investigation show clearly 

 that on the other hand we have in the nymph of Plathemis lydia 

 a very special and complex distribution of tracheae in some 

 respects especially adapted to aquatic larval life and changing to 

 simpler conditions in the adult. Lubbock states that the distri- 

 bution of the tracheae depends on the size and shape of organs. 

 Yet in the nymph of Plathemis lydia there are certain complexi- 

 ties that are not thus easily explained. For example the tracheae 



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