82 MR. walker's catalogue of iiomopterous insects 



M. Nilsson has given a coloured figure of a duck in this state of 

 plumage, plate 163, which is called a barren female, and in which 

 the curled tail-feathers are made very conspicuous. 



From the general similarity in these females to the appearance 

 assumed for a time by healthy males in July, I am disposed to 

 refer this seasonal change in males, in this and in other species 

 of ducks, to a temporary exhausted state of the male generative 

 organs, and their consequent diminished constitutional influence 

 on the plumage. 



A male shut up by himself from early spring to the end of July 

 undergoes no change in his plumage ; but if he is allowed to 

 associate with females till their season of incubation commences, 

 he then goes through the change, and this appears to indicate the 

 cause of the partial summer moulting. 



The appearance is somewhat different, but yet very interesting, 

 in Insects and Crustacea. In these classes the sexual organs are 

 double, and distinct, arranged one on each side of the elongated 

 mesial line. It sometimes happens that a species in which the 

 sexes are of a different colour, or markings, or form, has one 

 sexual organ of each sort, male and female, in which case each 

 half of the same insect is developed under the exclusive influence 

 of the sexual organ on its own side. Instances are preserved 

 among our collections of butterflies, moths, and beetles ; and I 

 have seen it twice in the common lobster. 



JNor is the human race exempt from the operation of the law 

 which prevails in the Mammalia. In women, at an advanced age, 

 hair appears on the chin and upper lip, and the voice alters, be- 

 coming deep in its tone. The beard in old men becomes thin and 

 soft, and our own inimitable Shakspeare has told us, 



. . . . " his big manly voice, 

 Turning again toward childish treble, pipes 

 And whistles in his sound." 



Catalogue of the Homopterous Insects collected at Singapore and 

 Malacca by Mr. A. E. "Wallace, with Descriptions of New 

 Species. By Francis Walker, Esq., F.L.S. 



[Read May 6th, 1856.] 



To carry out the object I had in view, as explained in the note to 

 Mr. "Walker's paper on the Diptera of Singapore and Malacca, 



