Larvae and Pupae 67 



both ends and extending from the head to the last 

 segment. This tube is so transparent that it can be 

 detected only by its motion, which churns the blood 

 about. The nervous system is a double chain of 

 ganglia on the under side, too transparent to be seen 

 in the living larva. There are two " salivary glands " 

 lying close to the esophagus in the head. The eyes 

 are simple, with no lenses, being a sort of transitional 

 stage between simple and compound eyes. 



Mouth-Parts and Food-Habits. — The mouth- 

 parts are very complicated arrangements. They con- 

 sist of the rotary brushes, labrum, mandibles, maxillae, 

 and labial plate. As might be expected, these follow 

 the usual rule of nature, that a difference in the 

 structure of the mouth-parts is correlated with a 

 corresponding difference in the food-habits. This 

 fact first forced itself upon the writer's attention 

 when studying the habits of the Louisiana species, 

 and was later confirmed when making dissections 

 and drawings of larvae of additional species for the 

 forthcoming Carnegie monograph on mosquitoes. 



The larvae fall into the two following categories: 

 (1) Insectivorous, which, like Megarkinus and Psoro- 

 plwra, normally prey upon small aquatic larvae of 

 other species of diptera, of other mosquitoes, and, 

 when hard pressed for food, even upon individuals 

 of their own species. (2) Non-insectivorous, which 

 feed on Euglena and other protozoa, bacteria, dia- 

 toms, slimes, algae, and other vegetable matter, 

 also at times upon minute Crustacea, such as the 

 water-fleas. The members of this class seem to have 

 a habit of swallowing grains of sand, and some of 



