1888.] 45 



The last two sub-families are divided according to the formation 

 of the anal characters, but it will be more convenient to describe these 

 in detail on another occasion, when I propose to offer some observa- 

 tions on the differential characters of the terminal segments from a 

 comparative point of view, with reference to the whole family, and I 

 will therefore now merely submit a few remarks with reference to the 

 Diaspince, and especially in regard to those filamentary secretions 

 which are usually termed the scales. The glandular organs with which 

 the insects are provided for secreting the scale material, I propose to 

 describe when treating of the terminal segments and the organs pe- 

 culiar to them. 



The scales of the Diaspince are usually of a filamentary nature, 

 occasionally weaved up together with what appear to be small portions 

 of the bark of the food-plant ; for example, the scale of Aspidiotus 

 ostreceformis has this appearance. The colour of the scales is usually 

 of a whitish hue, sometimes snowy-white, sometimes an ashy-grey. 

 It may here be mentioned that besides the scale properly so called, 

 and which is on the dorsal side of the insect, many species have a 

 ventral scale, which appears to be of a similar nature to the dorsal 

 scale. In some cases (e. g., Aspidiotus nerii) it is a mere film observed 

 on the leaf or bark after removing the insect. In other cases (e. g., 

 Aspidiotus rapax) it adheres to the insect when this is removed, so 

 forming a complete covering to it on the ventral side. The form of 

 the scales is variable ; they may be either circular or linear, or may 

 represent various modified shapes ranging between the two. When 

 the scales are round, the exuviae are usually situated in the centre, but 

 at the end when they are linear, in other words, when the scale is 

 circular it is spun all round the insect, and when it is linear it is spun 

 only at the posterior end ; and, judging from the shape of some, 

 e. g., Mytilaspis pomorum (fig. 4), I am led to suppose that the scale 

 is gradually pushed outwards, so that the most posterior part of the 

 scale of Mytilaspis would thus have been the first to have been spun. 



Professor Comstock mentions (Eep., 1880, p. 279) that some 

 species do not shed their first skin until they have already commenced 

 to secrete their scale, in which case the first larval skin cannot be 

 observed, as it becomes covered by the secretion. In other species the 

 larval skin is shed before the commencement of spinning, and it is 

 then plainly visible either in the centre of the scale as in Aspidiotus 

 nerii (fig. 6), or at one extremity as in Mytilaspis pomorum (fig. 4). 

 It will be remembered that the female casts its skin twice, and the 

 male only once. As a rule, the male scales are more elongated than 



