NATURAL HISTORY IJVRK IX CART AGO 57 



was found to be a miscalculation. Not only had the larger 

 devoured many of the smaller, but in addition, when the 

 pail of water was poured into a flat dish and left to settle, 

 there appeared incredible numbers of green hydras. These 

 attached themselves to the sides of the dish in such quantities 

 that they looked like green moss; they were equally thick 

 all through the mass of mud that had been gathered in with 

 the larvae. Even the larvae themselves were adorned with 

 them. I found hydras attached to heads, eyes, antenna, 

 wing-pads, legs, abdomens and gills, sometimes so thickly 

 clustered that I thought the larv« were green-striped or 

 spotted. These hydras ate up all the smallest kinds of food, 

 the copepods and daphnids, so that it was soon neccessary 

 to go out for more. 



If a larva in rearing showed signs of being ready to trans- 

 form we usually removed the twig with the larva upon it to 

 a dry netted tumbler so that the perfect insect could not 

 fall back into the water and drown or soak its wings before 

 they hardened. Occasionally this happened during our 

 absences but we had few accidents of that kind. Owing to 

 the elevation of Cartago we had little difficulty with mould 

 and mildew, while cockroaches and ants did not give us 

 anything like the trouble we would have had at a lower 

 location, so that we were able to preserve our specimens 

 with the minimum of labor. 



Of the dragonflies which we found in the immediate vi- 

 cinity of Cartago, three species were especially familiar, 

 as they occur also in the eastern United States. Two of 

 these were species of Pantala, flavescens and hymencea, large 

 insects of strong flight, with a wing-spread of almost four 

 inches and the hind wings very broad at the base; the former 

 with a yellowish body and some yellow at the base of 

 the hind wings, the latter predominantly olive and with a 

 rounded brown spot on the hind wing base. Both have an 



