1895.] COlOim-VAIMATIONS OF A BEETLE. 855 



case of the yellow, which is a distinct colour, there must be an 

 alteration in the nature of the pigment. 



Specimens are occasionally found having the elytron of one side 

 red and that of the other side yellow (fig. 31). Not very rarely 

 also there are more or less distinct patches of yellowish colour on 

 the red ground, as in fig. 32, where they happen to be nearly 

 symmetrical. These specimens are included in the Tables under 

 the head of " unconformable." 



In addition to the varieties already mentioned, there is also a 

 series of melanic forms. We have seen that the black pigment of 

 the elytra may either take the form of stripes or of spots. From 

 the latter group (fig. 1) a noticeable series of variations leads to a 

 form totally black above and below. Such a series is illustrated 

 by the figures 7-12 and 15-18. The first step in the progressive 

 pigmentation consists in the appearance of black in the positions 

 of the stripes, which is gradually extended. These specimens are 

 thus both spotted and striped. The parts last invaded are the 

 apices, the shoulders, and the borders of the elytra^ The spread of 

 the black is perhaps never quite symmetrical on the two sides and 

 is not rarely noticeably asymmetrical to the degree shown in the 

 figures. 



The series of progressive pigmentation is closely parallel to that 

 seen in Coccinella htjninctata, the common Lady-bird. 



Though the invasion of the black pigment proceeds along 

 tolerably regular lines, darkening the parts of the elytra in a 

 fairly constant order, yet as regards quantity of pigment varia- 

 tion towards the black form proceeds continuously, the states 

 becoming successively rarer as the full black is approached. From 

 the fact that the progress is so even it is not easy to give 

 numerical expression to this ; but on sorting the specimens which 

 have more black than fig. 1, it is found that while there are many 

 which approximate to figs. 7 and 8, there are fewer which resemble 

 figs. 9 and 10 ; those with only a few specks of red, Mke fig. 11, 

 are still rarer, while the totally black state is rarer than any of the 

 others. 



The darkening of the head and thorax proceeds more or less 

 evenly with those of the elytra, but the correlation is not strict. 



These melanic forms are, as has been said, an offshoot of the 

 spotted kind and not of the striped. They have red as the ground- 

 colour almost without exception. Fig. 26 represents the darkest 

 specimen I have seen with greenish ground-colour. 



A few specimens are found without any black markings on the 

 elytra at all. These have the undersides testaceous. In such 

 specimens the thorax has generally very little pigment and is 

 occasionally entirely without any. 



' Curiously enough, the two specimens figured by Olivier, Hist. Nat. des 

 Insectes, pi. viii. fig. 127, c and d, are both of these very melanic forms. The 

 locality is not given, and perhaps the frequency of the varieties may differ 

 with locality. 



