238 A YEAR OF COSTA RICAN NATURAL HISTORY 



Mecistogaster or its ancestors which would persist even when 

 the water-surface was much below the level of the epiphytes. 

 Only such plants as could retain water for long periods of 

 time (weeks and months) would permit the development 

 of essentially aquatic larvae and the water must be renewed 

 from time to time. Once the association of this insect with 

 bromeliads or any other suitable plant was formed it might 

 persist with the spread of the insect away from the regions 

 of deep yearly inundation, — the Amazon or wherever we 

 conceive its possible origin to have occurred — to the forests 

 at Juan Viiias where the trees which harbored our larvae 

 were far, far above the highest flood marks of the Rio Rev- 

 entazon. M. modestus, M. ornatus and Megaloprepus coeru- 

 latus, as we saw them in Costa Rica, usually fly above the 

 underbrush and when disturbed rise many feet above the 

 ground. 



Although all dragonflies have the abdomen in the winged 

 stage much longer than in the larva, modestus and, very 

 probably, all Anormostigmatini are extravagant in this 

 regard. In one modestus the fully extended adult abdomen 

 alone was 71 mm. long while the whole body in its larval 

 condition was but 20 mm. The abdomen of the adult 

 modestus is from 53^ to 53^ times as long as that of the 

 abdomen of the exuvia which it has just left, while in no 

 other Zygopterous species with which we are acquainted 

 is the corresponding figure more than 4^/^. In this latter 

 case {Philogenia carrillica, whose larva is not bromeliadic- 

 olous) the adult abdomen is 42 mm. long as contrasted with 

 a minimum of 63, for our Costa Rican modestus. 



The excessively long abdomen of the adults of all the 

 Anormostigmatini may be a special adaptation to the life 

 of their offspring in water-containing plants, since the abdo- 

 men of the larva of M. modestus is no longer, proportionally, 

 than in other Agrioninae. The space between one leaf of a 



