REPORT ON MOSQUITOES. 21 



The ninth abdominal segment is very small, furnished with a 

 series of long hair tufts arising from a ridged or barred area. It 

 is also furnished with one or two pairs of anal tracheal gills, 

 varying much in appearance as between species and somewhat 

 in length, within specific limits. In by far the greater number of 

 species these gills have no breathing function whatever, and 

 under the microscope no trace of trachea or breathing tubes are 

 seen. But there are a few species in which these organs are 

 functional, where the trachea are developed and where the larva 

 can get- all the oxygen it needs from the water itself. In the 

 case of the pitcher-plant mosquito, which lives a long time in the 

 larval state, specimens were kept in a jar under an oil film for 

 thirteen days without coming to harm. 



In attempting to identify mosquito larva the first point to be 

 regarded is the antenna ; has it an off-set or not ? Next, which- 

 ever way the decision goes, the length of the breathing tube and 

 its general proportion comes into question. Then the maculation 

 of the heacl and beyond that the scale-patch and pecten must be 

 referred to. It is not so easy as identifying the adults ; but on 

 the other hand the habits of the larvae and the place and time 

 where found often give a clue to the species that serves for ready 

 identification : i. e., if the larvae were found on a salt marsh, they 

 must be one of four species, which are easily distinguishable. If 

 they were taken upland these species are cut out from considera- 

 tion, and so, by taking habits as well as structure into account, 

 a very close approximation to the true species may be made in 

 most instances by any reasonably persistent student. 



THE PUPAL STRUCTURE. 



The term pupa is applied to that stage in the mosquito life 

 cycle which is intermediate between the larva or wriggler form 

 and the adult mosquito. In this stage no food is taken, though 

 the insect yet remains a water inhabitant. There is no resem- 

 blance to the original larval condition and, at first sight, not much 

 to the future adult. We have a hunched up creature without 

 obvious organs of any kind that floats on the surface of the 

 water when undisturbed and darts wildly and aimlessly through 

 the water with a jerky motion propelled by a pair of flattened 

 gills or swimming paddles situated at the end of the abdomen. 



If we examine this pupa more closely, looking at it from the 

 side, we begin to make out something of the future adult. The 

 flexible abdomen is more like that of the wriggler, except that it 

 does not end in a breathing- tube and does have the flattened 



