^-^ AND ^/ii^ 



JOURNAL OF VARIATION. 



Vol. IX. No. 6. June 15th, 1897. 



The development of the wing, wing=scales and their pigments 

 in Butterflies and Moths.*-' ^ Illustrated by Plate j. 



By J. W. TUTT, F.E.S. 



I.— The development of the wing and wing-scales. — A short 

 time since, we gave a brief account of the development of the Avings of 

 lepidoptera {Ent. liec, viii., p. 111). In it we stated that Verson had 

 found traces of wings in the embryo caterpillar of Bomhyx mori some 

 days before it leaves the egg, when the wing consists of a few cells in close 

 propinquity with a tracheal branch placed in the interior of the wall 

 of the body on the meso- and post-thoracic segments. Landois (1871) 

 and Pancritus (1884) discovered the rudimentary winglets in young 

 lepidopterous larvjc only 4min. long. At this time they appear as 

 infolded hypodermal pockets, penetrated by tracheae. When the larva 

 is full grown it is evident that the wing is really a folded portion of 

 the hypodermis {lidnn., PI. iii., fig. 1) itself, enclosing a thin layer of 

 mesodermal tissue {mbr. m., PI. iii., fig. 1). The conditions, however, 

 are complicated. The wing-pad proper is a pocket-like owrfolding of 

 the hypodermis, which is more or less folded upon itself. This 

 pocket, instead of lying exposed between the hypodermal covering of 

 the larva and its cuticula, is protected by being sunk into a deep sac- 

 like /((folding of the hypodermis, the walls of which are very much 

 thinner than those of the wing-pad, and, indeed, thinner than the rest 

 of the hypodermis. The walls of the infolded sac follow quite closely 

 the foldings of the wing-pad itself. In penetrating, from without 

 inward, one would traverse, in the region of the wing-pad, five layers 

 of the epidermis : (1) The outer and inner layers of the operculum- 

 like fold of the hypodermis which covers in the wing, then, in 

 succession, (2; the thick outer and inner layers of the wing-pad, and 

 (8) the thin inner layer of the infolded sac (Mayer). 



The trachere ftr., PI. iii., fig. 1) penetrate between the two 

 thickened layers of the wing-pad, the outermost layer being destined 

 ultimately to form the upper wall of the future wing, the inner layer 

 becoming the lower wall. The cells which compose the wing-pads 

 are more crowded in the longitudinal direction than in the direction 

 across the wing. The cells forming the tissue at this time are spindle- 

 shaped hypodermal cells (PI. iii., fig. 2). When the larva changes 



* A critical summary of a i^aper on " The development of the wing-scales and 

 their pigment in butterflies and moths," by Alfred Goldsborough Mayer [Published 

 at The Museum, Cambridge, Mass., U.S.A.]. 



