NORTH AMERICAN ODONATA. 152c 



insects. It has not been possible to answer such questions satisfac- 

 torily, owing to the lack of any work, in English at least, which 

 treated of the structure and development of the Odonata, save in a 

 brief and general way. Part I of the present paper is intended to 

 supply this deficiency, and, by mentioning those topics on which 

 present knowledge is insufficient or wanting, to suggest subjects for 

 investigation. It has been taken for granted that those who will use 

 it are already acquainted with the structure of insects in general and 

 the technical terms used in connection therewith, to at least the ex- 

 tent contained in the introductory chapters of Comstock, or of Pack- 

 ard, or in the papers on " Elementary Entomology" contributed by 

 the writer to Entomological News from May, 1890, to April, 1891 ; 

 and in treating of the embryonic development a knowledge of the 

 elementary facts of embryology is presumed. While free use has 

 been made of the existing literature in its preparation, by far the 

 larger portion of Part I is based on personal dissections, and some 

 details are introduced which are believed to be new, e. g. the descrip- 

 tions of the cephalic muscles (pp. 171-2), main tracheae (p. 179), 

 development of the skeleton of the nymph (pp. 195-8), and the view 

 of the phylogeny of the subfamilies (pp. 211-214). 



The writer is indebted to his brother, Mr. Frederic B. Calvert, for 

 the table on page 208. As stated in the text, this table is based on 

 Mr. Kirby's Catalogue, but it is highly probable that many of the 

 species contained therein will hereafter prove to be mere varieties, so 

 that the figures in the table rather overstate the facts. 



Valuable aid has been rendered by Mr. Chas. W. Johnson in sup- 

 plying specimens and dates ; by Dr. G. H. Horn, in comparing speci- 

 mens of Diplax with the types in the Museum of Comparative Zo- 

 ology at Cambridge, Mass. ; by Mr. Samuel Henshaw, in a similar 

 way for Aeschna clepsydra and Libellula exusta in the same museum ; 

 while Mr. H. F. Moore opportunely presented the nymph of Calop- 

 teryx maculata (afterwards raised to an imago) figured in part on 

 Plate II, fig. 8. 



Fig. 2 is after Walsh, figs. 33 and 34 are copied from Korschelt 

 and Heider's Lehrbuch ; all the others are original. 



Biological School, 

 University of Pa., 

 Philadelphia, Sept. 19, 1893. 



