FERRIS: MINUTE INSECTS 521 



certainly no more than one fourth of those which actually exist. In other words, 

 there are probably from 12,000 to 30,000 species of scale insects in the world. 



It is evident that sound and usable basic work on these mostly microscopic 

 forms is imperatively called for. Unfortunately, much of our present knowledge 

 is merely names, for only a relatively small portion of the named species can defi- 

 nitely be recognized on the basis of the existing work. It was not until about 

 1915 that methods of preparing material were developed which would make it 

 possible to see everything that is to be seen upon these insects and that a reali- 

 zation of the need for a genuinely suitable method of illustration developed. 

 Thus an important part of the work now before students of the group is the elu- 

 cidation of the mass of unidentifiable species, their proper illustration, and their 

 arrangement in genera which have some relation to the realities and will make 

 possible a fuller understanding of such problems as the geographical distribu- 

 tion of the groups and species. 



In the last twenty-five years especially, significant progress has been made. 

 The study of the Coccoidea has passed very largely from untrained amateurs 

 who might be called simply "naturalists" to a smaller but more competent group 

 of students with a definitely professional point of view, who are beginning to 

 achieve some results in the program of basic studies. The genera are being eluci- 

 dated as rapidly as circumstances permit and we are approaching the time when 

 students of the future will have a sound foundation on which to build. 



The Anoplura or Sucking Lice 



The Anoplura constitute another group which can be studied only from 

 material that has been properly prepared for examination under the compound 

 microscope. Almost all of the species are less than five millimeters in length. 

 Moreover, most of them are quite delicate forms which shrivel badly if they 

 are preserved in the dry condition. 



These, especially, are forms which have no attraction for those whose inter- 

 ests are determined by aesthetic considerations. As far back as 1842 a writer 

 remarked that he had often been rebuked by his friends for entering upon the 

 study of a group of insects whose very name was sufficient to excite feelings of 

 disgust. Hence the group received but little attention until about 1900, and as 

 late as 1908 a catalogue of the order listed only 65 species. We now know be- 

 tween 225 and 250 species, probably about half of those in existence. 



The connection of these insects with the transmission of disease makes the 

 group especially important, and the proper description and illustration of the 

 various species, which alone will make possible their precise identification and 

 a knowledge of their distribution and of their hosts, is urgent. 



The sucking lice have long been known because of the occurrence of two of 

 their species upon man himself, but as a group they also were long confused 

 with other wingless insects. Thus Linnaeus, who applied the old Latin name 

 Pediculus to them as a scientific name, included under this name a large and 

 weird list of species, many of which actually belong to quite different groups. 

 It was not until 1806 that the distinction between the biting lice and the sucking 

 lice was recognized and the biting lice were placed in a separate genus. Not until 

 1815 were the sucking lice themselves divided into three genera, not until 1844 



