24 



THE CALIFORNIA SPECIES OF MEALY BUGS 



some of these modifications being shown in text figure 15. In all the 

 Pseudococcine forms the inner end of the basal portion of the duct is 

 truncate and never reflexed into a cup, a character which I consider to be 

 distinctive of this group. 



J 



Fig. 15. Diagrams of optical, longitudinal sections through ducts typical of: A, 

 Eriococcus; B, Kermes; C, Pseudococcus; D, Lecanium. 



These cylindrical ducts of the Pseudococcine forms present some 

 features that may be used as specific criteria. Two rather distinct types 

 are commonly to be found. In one of these the ducts are relatively large 

 and the mouth is usually surrounded by a definite raised rim, while in 

 the other the ducts are smaller and lack this rim. The relative numbers 

 of these types is perhaps of specific importance, but is usually difficult to 

 express and therefore chiefly of value in the direct comparison of speci- 

 mens. 



In some species the cylindrical ducts may be of a distinctive type, 

 examples of this being seen in such species as Phenacoccus stachyos, 

 Phenacoccus kuwanae and Pseudococcus virgatus. In Phenacoccus 

 stachyos and Pseudococcus virgatus these ducts are strikingly large and 

 in the first named species their mouths are borne at the apices of conical 

 projections. In both of these species a conspicuous character of the liv- 

 ing insect is the presence of numerous glassy, waxen threads, which 

 undoubtedly originate from these ducts. In Phenacoccus kuwanae the 

 cylindrical ducts are conspicuously short and stout. 



The glands which do not possess cylindrical ducts discharge their 

 secretions through various types of dermal pores. Certain of these types 

 seem to appear in practically all of the Coccidae, while others seem to be 

 confined to particular groups. The extent to which they may be relied 

 upon in forming conclusions in regard to the limits of these various 

 groups can not be discussed here, for only a very extended study could 

 give such conclusions weight. However, they do appear to have certain 

 values within the group here under discussion that may well be con- 

 sidered. 



