ANTENNAL SENSE-ORGAN 29 



short hairs and they are further ohscured by the presence of scattered equally 

 coarse hairs among the general pubescence of the shaft. 



The antennge of Dinanamesus are intermediate in character between the forms 

 just discussed and the ordinary culicine type, both as regards length and the 

 nature of the hairs. 



In the Sabethini the antennae of the two sexes are usually similar and those 

 of the female may in many cases be characterized as sparsely plumose. In the 

 genus Johlotia, however, the antennae approach closely the culicine type. In the 

 female the hairs of the whorls are longer than in the culicines and there is a 

 crowding of cilia towards the tip of the joints, giving the effect of a small apical 

 whorl. In the male Johlotia the antennge are densely plumose but differ from 

 the common type by having the whorls basal and by having the penultimate joint 

 densely clothed with long hairs. In the common type of sabethine antenna the 

 joints of the shaft are slender, cylindrical, Avith a basal whorl of long hairs and 

 an apical whorl of short hairs. The apical whorl is a modification of the general 

 pubescence of the joint and is variously developed according to the species. The 

 shaft of the male antenna is often longer and more slender than in the female. 

 When the hairs of the whorls are sufficiently abundant the female antennae 

 appear sparsely plumose, like those of the male. The last two joints of the male 

 antenna are somewhat longer than the preceding ones, but these differences are 

 less marked than in the culicine forms. This lengthening of the last two joints 

 also occurs in the females of some species, but usually it is only the last joint that 

 is longer in this sex. 



The globose second antennal segment, as we have already mentioned, is a 

 highly developed organ of sense. Child has investigated this organ anatomically 

 and histologically in the most careful manner, not only in a number of Nemocera, 

 including Culex, but in insects of other orders. He succeeded in tracing the 

 organ, variously modified, in nine different orders of insects. The organ reaches 

 its highest development in the Nemocera, and, as it was first recognized as a 

 sense-organ by Johnston, Child has named it Johnston's organ. The function 

 of this organ has been frequently discussed. As our present knowledge of mos- 

 quito habits tends to modify the generally accepted ideas regarding its function, 

 a description of the organ itself is essential. We translate this, as far as seems 

 necessary, from Child's classic paper, and adhere to his procedure in first de- 

 scribing the organ in Corethra (Mochlonyx auct.), a non-biting culicid, and 

 following with a comparative description in Culex. The conditions in the male 

 of Corethra culiciformis are as follows : 



" The cup-shaped second segment is 0.15 mm. in length and 0.25 mm. broad. 

 The hollow of the cup, in which the shaft is attached, measures 0.08 mm. in 

 diameter and is 0.05 mm. in depth. The outer surface of the segment is densely 

 clothed with very small setae and in addition with a few larger ones. This seg- 

 ment rests upon the annulate segment which is hidden in the anterior surface 

 of the head, so that the movement of the entire antenna is brought about by the 

 muscles attached here. 



" It is this second segment which contains the sense-organ in question, Johns- 

 ton's organ, an organ of great development and verj?^ complicated structure (pi. I, 



