378 MORPHOLOGY OF THE ABDOMEX IX THE ODOXATA 



taneous study of stained specimens. Whenever posvsible this 

 method was used. 



The equipment used in the stud}- of the material included 

 microscopes of three types: a dissecting stand with three triple 

 aplanat lenses (37, 25, and 13 mm.), a camera lucida, and arm 

 rests; a binocular microscope with 48 and 32 mm. objectives 

 and No. 10 ocular; and a standard compound microscope. 

 Nearly all the work was done and fine measurements taken under 

 the binocular microscope". The camera lucida and dissecting 

 microscope were used in sketching outlines. 



ACKNOWLEDGMEXTS 



It is with i^leasure that I acknowledge the many advantages 

 offered me at the University of Pennsylvania. Dr. C. E. Mc- 

 Clung has extended to me ever}" facility the Zoological Labora- 

 tory afforded. To Dr. Philip P. Calvert I am most deeply in- 

 debted. He has not onlj^ placed material and equipment at my 

 disposal but has given freely of his time and of his wide knowl- 

 edge of the Odonata. The unlimited use of the library' of the 

 Academy of Natural Sciences of Philadelphia has been of very 

 great value. 



Comparative Ax'atomy 



review of the gexeral anatomy of the odoxate abdomex 



Before entering upon a specific treatment of the anatomy of 

 different forms it may be helpful to review the essential structures 

 of the Odonate abdomen. As this has been done bj^ other work- 

 ers (Calvert, 1893; Tillyard, 1917) but the barest outline need 

 here be set down. 



Imagoes 



In adults the general form is always elongate and cylindrical 

 or subcylindrical. Of the supposed twelve original segments 

 but ten are complete, the eleventh and twelfth being extremely 

 reduced. In the Zygoptera the diameter is quite constant 

 throughout the length, with slight enlargement in the basal and 

 apical regions, while in the Anisoptera some point in the central 

 region is widest and thickest, the form tapering towards the two 

 ends. In general the Zygoptera are cylindrical, the Anisoptera 

 dorso-ventrally compressed. 



