FERRIS: MINUTE INSECTS 519 



closely related matter of how to communicate to others the results of such study. 

 In other words, making suitable illustrations is equally a part of any work on 

 such forms. Here again, we must to a degree forget about any purely aesthetic 

 considerations. We must think merely of communication, for there is in such 

 specimens little artistic appeal. The present writer has been especially con- 

 cerned with developing methods of illustration which are peculiarly suitable for 

 this type of work. 



This paper, however, is not intended as a manual of methods. Its purpose is 

 to review the century's progress in the studies of the minute insects. But we may 

 legitimately call attention to the fact that this progress has depended entirely 

 upon the development of the methods discussed above. It is a sound generaliza- 

 tion to say that, in approaching such groups, the suitable solution of these prob- 

 lems of method is at least more than half the whole process. The dawning recog- 

 nition of this fact constitutes a large part of the story of progress in the study 

 of the groups to be discussed here. 



The Scale Insects (Homoptera: Coccoidea) 



Agriculturalists in California, Florida, and some other parts of the world 

 will be fully aware of the importance of these insects, for they are, in these areas, 

 among the most important of insect pests. In fact, horticulturists and green- 

 house operators almost anywhere will have had some experience with them. They 

 are almost all very small and this has been a significant factor in the develop- 

 ment of our knowledge of the group. The determination of the various species is 

 at times a matter of very great importance, but their positive determination 

 was long impeded by their diminutive size and by the failure to employ proper 

 methods, first in preparing them for study and then in illustrating them in 

 order to communicate the bases for their recognition. 



Certain aspects of the study of these groups are frequently confused. There 

 is a confusion between the fact that an insect has been named and the idea that 

 it has been described; again, there is a confusion between the fact that an insect 

 has been briefly described and the idea that it is "known." Approximately three 

 thousand species of scale insects have been named; relatively few of these are in 

 any real sense described and still fewer can be regarded as known. Actually, a 

 small percentage of the named species of scale insects are so described that they 

 can be identified positively from the original description alone. It is only in 

 recent years that methods of preparing these insects for study have been such 

 that they could be satisfactorily illustrated and perhaps even more recently 

 that proper methods of illustration have been developed. 



The story of the growth of our knowledge of the systematics of this group 

 is somewhat as follows. Linnaeus, in his Systenia Naturae, recognized only one 

 genus of this group, the genus Coccus. To this genus he referred 22 species. In 

 1784 the genus Orthezia was named, but for many years every one of the few 

 other species of this group that were described was referred to the genus Coccus. 

 Then in 1833 the genus Aspidiotus was named for all the forms which we now 

 call the family Diaspididae and in 1835 there was named the genus Diaspis, from 

 which the family name Diaspididae was derived. A very few genera were named 

 during the first two thirds of the nineteenth century, these almost always for 



