346 The Microscope. 



and membranous canals. The author thinks that the olfactory sense 

 is located in the sensory cones, and perhaps also in the membranous 

 canals, and that the hairs have a tactil function. The function of 

 the canals appears to be one which is well developed in a few insects 

 only, as they are only occasionally present ; where they are 

 found, they are present in large numbers. It is not likely 

 that they are of an auditory nature, but it is more probable 

 that they serve for the perception of definite odors, or fulfill some 

 unknown function. It is only in rare cases that it can be definitely 

 asserted that there is an orifice at the anterior end of the coaes, and 

 this point seems therefore to be of little physiological significance. 

 The chitin at the anterior end of the cone is in any case thin and 

 pale, and is probably affected by chemical and physical influences. 

 Treatment with diluted potash easily dissolves the chitinous mem- 

 brane, when the cone is laid open. Where the cones stand in chiti- 

 nous pits, and do not reach the surface, we cannot suppose that 

 there is any tactile function, but rather an olfactory. If this be so, 

 and there are different kinds of cones, we may suppose that these 

 have somewhat different functions. It is possible that some serve 

 for the perception of the feeble odors of distant objects, and others 

 for those that are nearer. 



On the palpi cones and hairs are alone found. Leydig was cer- 

 tainly justified in declaring that their anatomical structure shows that 

 the palpi have the same or similar functions to the antennae. Vom 

 Rath believes that the cones are olfactory organs, and probably 

 perceive not-distant odors. The cones on the maxilla, labium, 

 epipharynx and hypopharynx seem to be gustatory organs. 



The Unit of Microscopical Measurements. — Considerable con- 

 fusion has grown up of late, not only in this country, but in Eng- 

 land and Continental Europe by the use of the word " micromilli- 

 metre" as synonymous with "mikron," and thus designating the 

 micrometrical unit, viz: one one-thousanth part of a millimetre. A 

 paper on the subject from the pen of Prof. A. W. Ruecker, and pub- 

 lished in Nature (No. XXXVn, 1888, p. 388) calls attention to 

 the fact that by the action of the Royal Society on the report of its 

 Committee on the selection of Dynamical and Electrical Units, the 

 term mega is used to denote multiplication, and micro for division, 

 by one million; and hence as a mega millimetre would mean a million 

 millimetres, so a juicro-millimetre should, and does, signify one mil- 

 lionth of a millimetre. Micron or mikron, however, means the one- 



