Mr. Alfred R. Wallace remarked that Dr. Wallace's theory on the relation between the size of the specimen and the period of development satisfactorily accounted for the fact that as a rule in Lepidoptera the male was smaller than the female. Owing to the precarious tenure of life of a Lepidopterous insect, which was not only exposed to the attacks of many enemies, but was also liable to destruction from mere change of temperature, it was important that the female should be impregnated almost as soon as hatched, and therefore that males should be in readiness at the time of her emergence. The males which first hatched became the parents of the future progeny; the progeny inherited the qualities of the parent; and thus in process of time the males which had a tendency to early hatching, the small specimens which required a shorter period for their development, predominated, while those which hatched later, the larger males, being without mates and therefore leaving no offspring, would constantly tend towards extinction, and finally leave the smaller males in possession of the field.