836 



SCIENGK 



[N. S. Vol. IX. No. 233. 



appearance. This mining habit varies, of 

 course, with the plant, being less on per- 

 fectly smooth bark, and much more promi- 

 nent on bark that is rough or fibrous, or on 

 older wood. The same mining habit is ex- 

 hibited in scales occurring on leaves where 

 the epidermal growth or any sooty mold, 

 or other foreign matter, is lifted and covers 

 the scale in the same way. Several species 

 or sub-species of scale insects have been 

 established on accidental variations of this 

 character, as, for example, Chionaspis fur- 

 furus, var. fidvus King. Examples of the 

 type of this species sent to the Department 

 of Agriculture exhibit many scales which 

 show none of the epidermal coverings, while 

 others, owing to the character of the adja- 

 cent bark, are covered more or less com- 

 pletely by the outer layer of the bark of the 

 plant. On this basis any scale insect al- 

 most may be split up into two or three 

 species or varieties. The careful study of 

 the scale in its relation to its situation on 

 bark or leaf made by the writer has shown 

 that the majority of the species in the 

 Diaspinae occasionally or frequently present 

 epidermal or extraneous coverings. 



The scale varies also in shape as influ- 

 enced by the nature of its surrounding con- 

 ditions. The exuviae is often shifted, or ap- 

 parentlj' so, by obstructions, such as veins 

 or inequalities of the surface or the prox- 

 imity of other scale insects. A convex scale 

 becomes flattened when the insect occurs 

 beneath the sheaths of the leaves, as on 

 palms or bananas. 



Color also varies very notably, being in- 

 fluenced undoubtedly by climatic condi- 

 tions, dryness or humidity, the presence of 

 mold or other fungi. The food of the in- 

 sect on diiferent plants undoubtedly also 

 afifects the character of the excrements. 

 The effect of weather and age in bleaching 

 or otherwise changing the appearance of 

 the scale is often notable. The character- 

 istic appearance of the scale varies im- 



mensely in proportion as it has free room 

 for growth or is crowded or massed to- 

 gether densely on the bark or leaves. The 

 San Jose scale, growing in scattered numbers 

 here and there on the terminal twigs, bears 

 no resemblance whatever to the crowded 

 masses on old, badly infested wood. The 

 same is true of almost any other scale insect. 



The covering scale, therefore, cannot be 

 taken as a criterion of very great value in 

 the separation of species, and by itself is 

 almost without value. The specific char- 

 acters must be found in the insect itself, 

 the scale covering furnishing indications 

 only of a rough sort. The describer of new 

 species who fails to notice the importance 

 of these sources of error, and sees a species, 

 a sub-species, a phj'siological species or a 

 variety, in every such accidental difierence, 

 greatly retards rather than advances the 

 knowledge of this group of insects. It 

 would be j ust as legitimate to describe as a 

 new species an insect found on the under 

 side of a leaf, as opposed to an insect found 

 on the upper side, as to designate as new a 

 species because a little extraneous matter 

 is adhering to its scale covering, or to 

 describe men as distinct species because 

 they wear difiereut colored coats. 



When the insect itself comes to be ex- 

 amined, other sources of error present 

 themselves. For example, the question of 

 the matui'ity or adultness of the specimens 

 under study arises, and also the problem of 

 individual variation. In the determination 

 of material it is, as a rule, absolutely neces- 

 sarj' to have the adult female insect. In 

 the Diaspinae, for example, the full grown 

 second stage of the female is often nearly 

 as large as the third or last stage, if not 

 larger in some instances, and yet the dif- 

 ference in the structural characters of the 

 two stages is verj' great. As an example 

 of a description of a new species from a 

 failure to recognize the maturity of the 

 specimens, Cockerell's so-called variety 



