204 PHILIP p. CALVEPvT. 



The range of size of Odonate images extends from Agriooiemis 

 minima Selys, of Java, whose abdomen measures 13.5 mm., the hind 

 wing 8.5 mm. — to the Central American Megaloprepus ccerulatus 

 Drury (ab. 102, hind w. 94) and the South American Mecistogaster 

 amalia Burm. (ab. 130, h. w. 85). The three species named are all 

 Agrioninae and have very slender bodies. The largest robust species 

 is Gynacantha plagiida Waterh. (ab. % 90, 9 67, hw. % {jo.5, 9 

 81), an Aeschnine of Borneo and Sumatra. 



3. Distribution of the Odonata. 



CONDITIONS determining DISTRIBUTION. 



Nature of the water in which the 7iyviphs live. — Owing to the aquatic 

 life of the nymphs, the imagos absolutely must spend at least a por- 

 tion of their lives in the neighborhood of fresh, or at the most, 

 brackish water. No Odonate nymphs are known to live in salt water, 

 but probably some coast species, such as Isehyiura Ramhurii and 

 Micrathyria herenice, live in that which is brackish. Schwarz ob- 

 served nymphs in shallow pools of mixed salt and sulphurous or 

 fresh water on the flats near Great Salt Lake, Utah, and in sulphur 

 creeks (Can. Ent. xxii, pp. 238-9). 



Temperature. — Considerable heat is required for imagination, for 

 activity during, and for the very existence of, imaginal life. Even 

 in temperate climes the Odonata are only active in warm weather, 

 cool, cloudy days in Summer causing them to take refuge in grass 

 and foliage. Only one species of Odonata — the European Sympycna 

 fusca Vander L. — is known to regularly hibernate as an imago in 

 numbers (Rene Martin, Rev. Sci. Bourb. i, pp. 53-57), although 

 some few imagos of Dip)lax do so. This ability means a greatly in- 

 creased length of imaginal life, which for most Odonata varies from 

 25-45 days, but in S. fusca becomes nearly seven months (Martin). 

 In the great majority of cases the Winter is probably spent in the 

 nymphal state. 



Checks to Increase. — Negative checks to increase may be due to 

 the drying up of the water in which unhatched eggs have been placed, 

 or to low temperature; the eggs do not seem to be well adapted to 

 resist unfavorable conditions, judging from those reared in glass jars, 

 although McLachlan found Agrion mercuriale ovipositing in soft 

 mud where the water had evaporated. Positive checks are furnished 

 by those animals which devour or injure the Odonata in difl^erent 

 stages. Brandt (18) found more than half the eggs of Calopteryx 



