SCALE INSECTS OF IMPORTANCE 353 



The chitinous processes are subequal on the two sides of each incision. 

 They are quite large beside the first incision but are somewhat irregular 

 in shape and usually not so strongly curved on the inner side as is the 

 case in A. perniciosus, and those on the inner edges of the median 

 lobes are variable, sometimes easily detected and in other cases vague 

 and indefinite. 



The ventral glands in the adult female are quite numerous and are 

 usually in compact, nearly circular groups, while those of A. ancylus 

 are more likely to be linearly arranged. Dr Marlatt gives the numbers 

 as averaging six for the anterior group, which is usually much the smaller, 

 and 10 or 12 for each of the lateral groups, but the numbers vary 

 quite considerably. 



The thickenings in the region of the ventral glands are indefinite and 

 look somewhat like crumplings or foldings of the body wall. 



The anus is small and quite distant from the median lobes. The 

 margins, however, run up to embrace it. 



Dr Marlatt says : 



The dorsal pores are quite characteristic. There are usually two 

 between the first pair of processes and a row of five or six extending 

 from the second pair of processes and after a considerable interval, con- 

 tinued near 'the lower group of paragenital glands in one or two addi- 

 tional pores. A lateral row of about 10 or 11 pores extends from near 

 the base of the first pair of spines to the lateral chitinous thickenings. 

 Diifering from most of its near allies, it has a group of six or seven pores 

 near the basal angles of this segment. 



In the next to the last sentence " first pair of spines " means the first 

 spines beyond those associated with lobes, as I think will be seen on 

 study of this figure. The number of these pores varies somewhat, yet 

 there is a certain characteristic general appearance in this arrangement 

 that becomes familiar and at sight suggests A. ostreaeformis to a 

 student of these forms. I have often found three pores in a group at the 

 first incision, and sometimes there are many more in each of the groups 

 than the numbers given above. I have found two lots on willow in our 

 collection where the number and closeness of arrangement of these pores 

 suggest A. juglans-regiae, so that Dr Marlatt, to whom the speci- 

 mens were submitted, advances interbreeding as a possible explanation 

 of the phenomena. The lobes are three on each side of the median line 

 in this willow form, and the ventral glands are more numerous than in 

 typical A. ostreaeformis, while the specimens are larger in size. 



In the second stage the two pairs of lobes are usually distinctly 

 present, though the second are minute. Sometimes a hint of the rudi- 

 mentary third ones can be discerned. The incisions are wide antl not 



