2 THE COCCIDAE 



pairs of mouth-parts, the mandibles and the maxillae, are long, 

 slender, bristle-like appendajjes that are similar in appearanee. 

 The third pair, the labium, is in the form of a long segmented tube 

 which is fitted for sucking and piercing and is known as the ros- 

 trum. This tube is normally folded against the ventral aspect of 

 the head and thorax. It contains a longitudinal furrow which is 

 open on the dorsal aspect. Tiie sides of this furrow are adjacent, 

 forming a lumen in which the bristle-like mandibles and maxillae 

 are held and supported. Each segment of the thorax bears a pair 

 of legs, which consist of the usual number of sclerites or segments. 

 The mesothorax and metatliorax usually bear also a pair of wings. 

 The thorax generally bears two and the abdomen a varying num- 

 ber, never more than eight and usually about six, pairs of 

 spiracles. Certain coccids lack all these features indicating rela- 

 tionship with the Hemiptera except the presence of two pairs of 

 thoracic spiracles and of a thin external body skeleton or cuticle. 



The great diversity and peculiarity in the form of many 

 coccids and the similarity to them in general external appearance 

 of certain species of some of the related families of Hemiptera has 

 led even some specialists into the error from time to time of 

 describing insects other than coccids as such. All orders of insects 

 can be divided into two large groups according to the number of 

 tarsal segments, in one group would fall those with five segments, 

 assumed to be the primitive condition, and in the other those with 

 less than five segments. The Hemiptera and the closely related 

 orders of Exometabola with sucking mouth-parts belong to the 

 grouji Avith less than five tarsal segments. This latter group can 

 be divided into two series upon the size of the pronotum and the 

 condition of the wings. In one of the scries the mesothoraeic wings 

 are modified into veinless wing-covers or elytra and the pronotum 

 is a large subquadrangular area loosely articulated to the 

 mesonotum, while in the other group the wings, altliough sometimes 

 thickened, are never modified into elytra and the pronotum is 

 reduced in size, collar-like and immovablj' united with the 

 mesothorax. The Ilemiptei'a and their allies, which belong to the 

 latter series, are easily sepai'ated from all other insects with tarsi 

 of less than five segments, because their mouth-parts, in immature 

 individuals as well as adults, are fitted for sucking. It is very 

 unusual to have inunature insects with sucking mouth-parts. 



The form and structure of the sucking mouth-parts of tiie 

 orders with less than five segments in their tarsi are suflBciently 

 distinctive and typical to diflFereutiate them from each other. T!u' 



