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THE AMERICAN NATURALIST. [Vol. XXXVIII. 



nection that in the tracheoles of developing wings, structures 

 entirely similar to those of the light-organs, the presence of air 

 may be readily seen. 



In sections parallel to the axis of the cylinder the tracheoles 

 are generally cut, so that their entire length cannot be followed. 

 The fact that they appear to end free cannot, therefore, be taken 

 as any proof. In rare cases they are seen to anastomose with 

 those of adjacent cylinders, and in sections transverse to the 

 cylinders, beautiful demonstrations of anastomosing may be 

 seen. If a light-organ from a freshly killed insect is placed for 

 a half hour in .5 osmic acid, then for a few minutes in caustic 

 potash, and then placed under the microscope, ventral side up, 

 the tracheoles can be easily seen. The cylinders stand out as 

 definite circular or oval rings, and from the inclosed tracheae 

 radiate the tracheoles. As the distribution of the cyhnders is 

 fairly regular, the network of tracheoles has a notably uniform 

 pattern. Tracheoles from three cylinders unite at a point about 

 equidistant from their respective cylinders. (Fig. 5.) In prep- 

 arations from material fixed in Flemming's, or Gilson's fluid, the 

 same tracheolar network may be clearly seen. (Fig. 6.) 



When the ventral surface of a fresh light-organ is studied 

 under the microscope in a dark room the light is found univer- 

 sally distributed through- 

 ^ " / / out the parenchymatous 



. ^ area. The cylinders stand 



. .ut as non-photogenic spots 

 on the background of light. 

 ^ This shows that the photog- 



■' J eny occurs in that portion 

 # of the tissue where the tra- 

 cheolar network is found, 

 and where there is conse- 



* ''^safmntr xTsf ^ tracheoles. Fleming's fluid, ^^^^j^^ly the mOSt abundant 



supply of oxygen. 

 Wielowiejski found anastomosing of the tracheoles generally 

 true in Lampyris, although he admits of some exceptions to the 

 rule. Wistinghausen and Holmgren found anastomosing of the 

 tracheoles in the silk-glands of the caterpillar. Emery states 



