MAYER: DEVELOPMENT OF WING SCALES. 211 
Scales; (3) The Probable Physical and Chemical Nature of the Pig- 
ments ; (4) A Summary of Conclusions believed to be new to Science. 
The material made use of in the research consisted of larvæ of Danais 
plexippus Fabr. and Pieris rape Linn., and pups; of Vanessa antiopa 
Linn., Danais plexippus Fabr., Pieris rapee Linn., Papilio turnus Linn., 
Papilio asterias Fabr., Callosamia promethea Linn., and Samia cecropia 
Linn. 
# The larvee were killed in Perenyi's fluid warmed to about 55? C. In 
the case of the pup the outer chitinous cuticula was peeled off from one 
of the wings, in order to allow a more perfect penetration of the killing 
fluids. The reagents used in killing the pupe were, (I) hot saturated 
solution of corrosive sublimate in 35% alcohol, (2) Perenyi's fluid 
warmed to about, 55° C., (3) P. Mayer's picronitric mixture, and (4) a 
saturated solution of picric acid in 50% alcohol. The best results were 
obtained from Perenyi's fluid ; corrosive sublimate, however, gave good 
histological results, but it often failed to penetrate the chitinous cu- 
ticula. Various stains were tried, such as Kleinenberg's heematoxylin, 
Khrlich’s haematoxylin, the Ehrlich-Biondi mixture, and safranin. All 
staining was done upon the slide, and the best results were obtained 
from Kleinenberg's baematoxylin, either alone or followed by safranin. 
The latter method brought out a sharp differentiation between the pro- 
toplasm, which was stained blue, and the chitin, which was tinged pink. 
Safranin was found to be an excellent stain for chitin. Paraffin sections 
were employed, and were usually 6.6 / in thickness. 
1. The General Development of the Wings and Scales. 
It appears from the researches of Landois (71) and Panoritius (84) 
that the Anlagen of the wings may be found in young Lepidopterous 
larvee only 4 mm. long. They appear in tho second and third thoracic 
segments of the larva as infolded hypodermal pockets penetrated by 
trachew. Figures 1 and 2 (Plate 1) give the appearance of a frontal 
section through the left wing of a mature larva of Pieris rape (Danais 
plexippus exhibits the same general appearance) viewed from above. 
Figure 2 is merely a diagrammatic reproduction of Figure 1, and is 
intended to show more clearly the manner in which the hypodermis is 
folded. In both figures, cta. indicates the outer chitinous cuticula of the 
larva; de., the hypodermis; d., anterior; p., posterior; and mbr. m., 
the middle membrane, which encloses the trachem. The thickened por- 
