SCALE INSECTS OF IMPORTANCE 



345 



speak of them simply as the ventral glands. They appear only in the 

 adult female and not in all species. They are of rather special interest 

 in economic study because their presence at once proves the specimen to 

 be something other than the pernicious or San Jose scale, though their 

 absence does not necessarily indicate the contrary. Once seen they are 

 easily recognized, for no other organ resembles them in their definite 

 circular outline and in the manner of grouping (pi. ii, fig. i g, g). In 

 the genus Aspidiotus there are usually four or five groups when pres- 

 ent at all. The groups are then spoken of as the anterior or cephalo- 

 laterals, and the posterior, or caudo-laterals, while the fifth group when 

 present is anterior and median and is called by the one or the other of 

 these terms. 



In the region of the lateral ventral glands the body wall is thickened 

 (pi. II, fig. ih). These are the ventral chitinous thickenings, and are to 

 a certain degree characteristic. In A. ancylus and A. ostreae- 

 formis they are somewhat indefinite and appear as if folded or crum- 

 pled, in A. forbesi they are nearly straight, narrow and definite, being 

 spoken of in the original description as "club-shaped organs about which 

 the spinnerets are grouped." In A. perniciosus also they are more 

 definite than in A. ancylus and A. ostreaeformis, though not so 

 straight nor so narrow as in A. fo rb e s i, and they appear distinct and 

 dark in the adult female even when the eggs or young are not present to 

 prove the species. This distinguishes the adult but not yet gravid A. 

 perniciosus from the immature specimens of the four species, because 

 in the first and second stages of all four these thickenings, though indi- 

 cated, are small and indefinite, practically parenthesis-shaped and quite 

 different from the third stage appearance. Reference to the figures will 

 make these statements perfectly clear, I think. 



The vagina may sometimes be detected as a tranverse opening about 

 the middle of the plate on the ventral side (pi. n, fig. y). It does 

 not in general serve in classification, and I have not figured it under the 

 different species. 



The dorsal aspect is marked near the base of the segment in the following 

 species by four, transverse chitinous thickenings, two lateral and two 

 median (pi. ii, fig. i k, k). Occasionally there are two fainter longi- 

 tudinal markings of chitin parallel and near the middle of the segment. 



There are also on the dorsal aspect oval openings of more or less 

 prominence in different species, which are perhaps most simply designated 

 the dorsal pores. I have shown different appearances of these seen in 

 focusing in plate ii, figure i /, /. In some species they arc numerous and 



