214 PHILIP p. CALVERT. 



phinse and Libellulinse have reverted to the far back aucestral peculiarity in 

 this respect. On the other hand, to accept Mayer's view means that the ephem- 

 erine appearance of the nymphs, the separation of the eyes, the cleft labium, 

 the completeness of the first lateral thoracic suture, and the distinctness of the 

 last two thoracic ganglia of the Calopteryginpe are all reversions. If the absence 

 of an ovipositor really be of great importance, the Gomphinse ought to offer more 

 primitive characters than the Libellulidse, but the view taken above seems the 

 most satisfactory to the writer. 



No embryological evidence for the solution of the question exists as yet. The 

 paleontological evidence, as already set forth, tells of the existence of Libellu- 

 linse, Gomphina? and Aeschninae in the Lower Lias, and nothing of the Calop- 

 terygiufe until the Oolite, but at the meeting of the Entomological Section of 

 the Philadelphia Academy of Natural Sciences, held May 25, 1893, at which the 

 writer brought the matter up for discussion. Dr. S. H. Scudder expressed the 

 opinion that the scantiness of fossil Odonata did not give weight to any negative 

 arguments based on their non-discovery. 



The writer had written the above statement of his views of the phyiogeny of 

 the Odonata before he had read the brief expressions of Kolbe and Redtenbacher 

 tending to the same opinion. Kolbe (Berl. Ent. Zeit. xxviii, p. 393, 1884) says 

 of the " Agrioninen" that they are of the lowest stage of Odonate organization 

 by their separated eyes, prothorax still moderately large, almost equal wings, 

 pterostigma differing rarely from the other cells, and external tracheal-gills in 

 the larvffi. Redtenbacher writes " While it seems doubtful to me to look upon 

 the Gomphidse as the oldest forms of the Odonata, I think that I recognize in 

 the wing of Caloptery.c that form from which the wing-forms of the other 

 Odonata are derived" (Ann. k. k. Naturhist. Hofmus. Wien, i, p. 167, 1886). 



Note on the Preservation of Specimens. 



For the ordinary systematic collection of dried Odonata, it is always advisable 

 to insert in every specimen, when it is mounted a bristle, or a fine non-corrosive 

 wire, beginning at the nasns and passing it through the entire length of the 

 body, but not allowing it to project beyond the eleventh (anal) segment. This 

 holds the various parts of the body together. The thickness of the bristle should 

 conform to the size of the specimen. If it be desired to preserve the coloring 

 of the body, it is of some advantage to make a longitudinal cut on the ventral 

 surface of the abdomen and even the thorax, remove the contents, and insert a 

 wad of cotton ; in doing so, the body wall must not be rubbed or scratched by 

 the instruments employed. Some specimens of each species should always be 

 preserved intact, as the cutting usually destroys or distorts some of the abdominal 

 structures, which are of more importance for study than the colors. Nymphs 

 and specimens for dissection may be preserved by killing them, or placing them 

 immediately after death, in hot, but not boiling alcohol of 50 to 60 per cent, for 

 three or four hours, then transferring them to (cold) alcohol of 75 to 80 per cent, 

 in which they may be kept indefinitely. N. B. — The vessel containing the al- 

 cohol to be heated must be placed in another vessel containing water and thus 

 heated indirectly to avoid the danger of explosion. For methods of technique 

 for histological purposes, recourse must be had to the histological papers quoted 

 in the Bibliography. 



