28 THE CALIFORNIA SPECIES OF MEALY BUGS 



that of the structures by which they are produced, a correlation that in 

 many cases can be directly traced. It is in fact possible to gain a very 

 accurate conception of the appearance of a species in life from a con- 

 sideration of its morphology alone and, conversely, it is possible to gain 

 some idea of the morphology of a species from a consideration of its 

 appearance in life. It is only in the light of this that most of the existing 

 descriptions are at all intelligible. 



The lateral waxy tassels or "filaments" which are so conspicuous in 

 many species of this group, are produced by the cerarii and their form 

 and size are directly dependent upon the nature of the cerarii. If the 

 cerarii are lacking there will be no tassels, and if there are no tassels the 

 cerarii are lacking or very weakly developed. If the cerarii contain a 

 large number of pores, cerarian spines or auxiliary setae, the tassels will 

 be strongly developed, and if the tassels are of unusual length or size 

 we may predict that the cerarii will present a corresponding development, 

 although we cannot say exactly .what form this development will take. 

 In other words, similar tassels may be produced by a quite different ar- 

 rangement of the various elements of the cerarii as is shown in the case 

 of Pseudococcus maritimus and P. citrophilus. 



The presence of glassy waxen threads such as appear in Pseudo- 

 coccus virgatus or Phenacoccus stachyos is unmistakable evidence of 

 the presence of some sort of large pore or duct, although the exact nature 

 of this pore or duct can not be predicted. I have been unable, however, 

 to trace the correlation between the presence of dorsal lumps of wax, 

 such as appear in Pseudococcus nipae and P. aurilanatus, and any mor- 

 phological elements, nor have I been able to account for the formation of 

 a complete sac in some species and not in others. It is possible that this 

 is dependent upon the physiology of the insect as is the case when the 

 wax is yellow instead of the usual white. The correlation between the 

 ovisac and the ventral glands by which it is produced is likewise too 

 subtle to be traced. I cannot say why the ovisac of one species is 

 loose and fluffy while that of another is firm, or why one is short and 

 another is long. It is by no means impossible, however, that sufficiently 

 careful and extended studies may throw some light upon these difficulties. 



BIOLOGY 



There has always been more or less of a tendency among students 

 of the Coccidae to name species on the basis of differences in host plant 

 and habitat. In a group such as this, where tangible structural differen- 

 ences are supposedly or actually few, it is difficult to resist this tendency, 

 yet it must be resisted if we are to avoid confusion of the most serious 

 kind. Essig, in separating his Pseudococcus bakeri from his previously 



