SUBFAMILY DIASPIDINAE f* 239 



& 



Malphigian tubules and poured out through the anus. In the 

 case of the dark or blackish scales the coloring matter is located 

 in the excretion from the Malphigian tubules. The remarkable 

 white varieties, as in the case of Lepidosaphes ulmi Candida, are 

 imperfect individuals which were unable to produce the secretion 

 necessary to color the scale. It is not unusual to find individuals 

 in large colonies containing many individuals in which the cephal- 

 ic half of the scale is normal in color, black or brownish, and the- 

 caudal half is white or uncolored. 



The English and some other writers usually designate the 

 exuviae as the pellicles, the first exuvia as the larval pellicle and 

 the second exuvia as the nymphal pellicle. Most American 

 writers usually employ a word derived from the Latin word 

 exuviae, which was used by the Romans to designate the cast off 

 skin of animals. It was used in the pleural only. Some writers 

 apparently do not differentiate between the cast skins of the first 

 and second nymphal stages and always use the word exuviae but 

 evidently only in the pleural form. Comstock and Cockerell em- 

 ploy the word exuviae for both female and male scales, evidently 

 using it in both a pleural and a singular sense. Some have used 

 a neuter form, exuvium, for the singular and the regular pleural 

 form, exuvia. These forms have found their way into the Ameri- 

 can dictionaries. Ferris writes of the first exuvium, the second 

 exuvium, and the exuviae. So far as observed, Cooley was the 

 first to use the singular form, exuvia. He is followed in this by 

 Marlatt. The regular Latin singular of exuviae would be exuvia. 

 These forms have been adopted. 



The scale consists of two parts, a dorsal scale, sometime 

 simply designated as the scale, and a ventral scale. The ventral 

 scale is frequently very thin and adheres closely to the surface 

 of the host-plant, but it may be well developed and fused with 

 the dorsal scale. As each exuvia is molted, it is secured to the 

 sheet of wax of which the scale is formed by a coating on its 

 inner surface. As the second exuvia is cast later, this explains 

 its position under the first, but there is always a sheet of wax 

 between them. In the case of those aspidiotids which rupture 

 their exuvia around the margin of the body, the dorsal portion 

 of the exuvia is imbedded in the dorsal scale and the ventral 

 portion in the ventral scale. Because the ventral portion of the 

 exuvia is thin and delicate, it is frequently overlooked, but in 

 many cases where the ventral scale is very thin, it is likely that 

 the ventral portion of the exuvia is lost. In all other Diaspidinae 



