102 MOSQUITOES OF NORTH AMERICA 



the wings. The same segmentation into femur, tibia, etc., is recognisable as in 

 the adult gnat, but the segments are more nearly equal in the pupa, and the 

 joints of the developing and shrinking legs of the future imago soon lose their 

 correspondence with those of the pupal cuticle enclosing them. They arise in 

 the larva, like other appendages, as folds of epidermis enclosing mesoblastic 

 tissues. 



" The abdomen is dorso-ventrally compressed and exceedingly flexible dorso- 

 ventrally, though not from side to side. It is the only part of the pupa in which 

 the segmentation of the body is readily recognisable, and as I shall very fre- 

 quently have to refer to the various segments by number, / shall use the terms 

 ' first segment' etc., to signify ' first segment of the abdomen ' etc. 



" Nine segments are readily recognised in the abdomen, and the last one, 

 though it is probably composed of no less than three condensed and highly modi- 

 fied segments, I shall call simply ' ninth segment.' 



" Each abdominal segment has a chitinous tergum and sternum, and setae are 

 distributed sparingly over them, being almost confined to the hinder parts of 

 the terga. The terga and sterna of successive segments are united by soft 

 arthrodial membranes. 



" Of the setce, only one pair need special mention. These are placed on the 

 hinder part of the first segment, the base of each being a triangular plate at- 

 tached by one angle to a soft membrane, and the distal side of the plate is divided 

 into a number of bars which, by repeated division or branching, give rise to about 

 one hundred setse all lying in one plane parallel to the median plane of the body. 

 Each seta bears a few fine hairs. When at rest, the pupa floats with the tips of 

 these setae, and the tips of the respiratory siphons, at the surface of the water, 

 and these setse probably assist in maintaining the equilibrium of the animal in 

 this position, as well as serving as sensor}'^ organs by means of which any dis- 

 turbance of the surface is felt. 



" The eighth segment bears a pair of large fins, thin oval plates about 1.2 mm. 

 in length, attached by the narrow end beneath the tergum behind. Each is 

 stiffened by a midrib which projects beyond the hinder border of the fin as a 

 spine. 



" Beneath the fins and behind the eighth segment is the 'ninth segment ' with 

 its appendages. Though this region is probably made up of more than one seg- 

 ment, its composite nature is not easy to recognise, as the plates supposed in 

 other insects to represent the terga and sterna of tenth and eleventh segments 

 [see, for instance, Huxley and Miall and Denny] are not developed in the young 

 pupa, nor, indeed, is there in any stage any such development of the pupal 

 cuticle, though plates developed within as parts of the imaginal cuticle may per- 

 haps represent some of these parts. 



"The appendages of the 'ninth segment' of the pupa are a pair of blunt 

 processes arising below and in front of the anus, and directed baclavards below 

 the fins. They are much larger in the male than in the female. A pair of ap- 

 pendages are already recognisable in this region in sections of the larva, and I 

 think even two pairs, but this portion of the larva is particularly difficult to 

 cut, and I am not yet certain as to the hinder of the two pairs. Of the existence 

 of one pair I have no doubt." 



Some mention must be made of the modifications of structure which occur in 

 the pupae of different species or groups of species. The early writers on the 

 biology of Anopheles made much of the difference in the shape of the respirator}' 

 trumpets between Anopheles and " Culex." Their statements appear to have 

 remained unchallenged and are still widely quoted. The variations in the shape, 



