146 INTKO1 V TO EXTOMO/.OGY. 



Figure 130 represent^ a common form of this segment. 

 But these special characters of tli .cut are not presented In- the 



larv.e till after the first moult, nor by the male alter the chan- 

 pup 



The following account of the metann>rplm>es of the Diaspin.r i> 

 quoted from my report on Scale-Insects in the Annual Report of the 

 U. S. Department of Agriculture for 1880. 



The newly-hatched scale-insect is oval in outline, much flattened, furnished 

 with six legs, a pair of antennae, and an apparatus for sucking the juices from 

 plants. (See Plate VI. \ouni; of . L\/> /<//<//// .* jit us.) At thi- 



its existence it is very small, a mere speck, which the untrained eye could only 

 with difficulty detect. By means of a lens, however, these minute creal 

 can be seen crawling in all directions over the leaves or bark of an int< 

 tree. After wandering for a time, usually but a few hours or e\en less, the 



ig scale-insect settles on some part of the plant, inserts its beak, and draw- 

 ing its nourishment from the plant, begins its growth at the expense of its host. 

 In a short time there begins to exude from the body of the larva fine tin 

 of wax, which are cottony in appearance. The excretion of this wax continues 

 until the insect is completely covered by it. The rate at which this excretion 

 is produced varies greatly. Thus larvae of the red scale of Florida (.ls/>/(//o/us 

 ficus), which were only one day old, were found to be completely covered by the. 

 cottony mass which they had excreted ; while the larvae of Glover's scale j.I/r//- 

 laspis Glwerit) did not become entirely covered until they were six days old. 

 Sooner or later the larva begins to excrete a pellicle, which, although 

 thin, is dense and firm in texture. The mass of cottony fibres either melts or 

 is blown away, or, as in certain species of Aspidiotus, a portion n -mains 

 white dot or ring on the centre of the scale. After a period, whirh, in several 

 species that we have studied, is about one-half of the time from the hatching of 

 the larva to the emerging of the male, or one-third of the time from the birth 

 of the female to the date at which she begins ovipositing, the larva sheds its 

 skin. In some species this does not take place until after the beginning oi the 

 formation of the permanent scale, and in such cases the moulted skin adhe: 

 the inner surface of the scale; and cannot be seen while it is in its normal posi- 

 tion on the plant. This is true of many species belonging to the genus Aspidi- 

 otus {A.ficus, A. citri, A. perniciosus, and othersi. In these -peeies the position 

 of the exuviae is indicated by a nipple-like prominence, often marked by a 

 white ring or dot, which is the remains of the cottony ma>s lir>t excreted. In 

 other species the moult takes place before the beginning of the excretion i' tin- 

 permanent scale. In these, the larval skin is plainly visible either upon t la- 

 surface of the scale, as in certain species of Aspidiotus (. /. .v,v //. ! and 

 in Diaspis (Plate VIII. Fig. M. 2,n. or at one extremity, as in Mytil.i-; 

 X. Fig. la). Sometimes, however, the larval skin is covered by a deli. 

 parent layer, which, I think, is the melted or compacted remains of the cottonv 

 mass excreted by the young larva (Plate X 



The change which the larva undergoes at this moult is a very remarkable 

 one, appearing to be a retrogression, instead of an advancement to a more 



