ANTENNAL SENSE-ORGAN 29 
short hairs and they are further obscured by the presence of scattered equally 
coarse hairs among the general pubescence of the shaft. 
The antennx 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 antenne of the two sexes are usually similar and those 
of the female may in many cases be characterized as sparsely plumose. In the 
genus Joblotia, however, the antennx 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 Joblotia the antenne 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, with 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 antenne 
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 (Mochlonyzx 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 sete 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. 
“ Tt is this second segment which contains the sense-organ in question, Johns- 
ton’s organ, an organ of great development and very complicated structure (pl. I, 
