EVOLUTION IN COLOR-PATTERN OF THE LADY-BEETLES. 



specimens shown in figs. 25, 16, aa, and 16, 66. In Epilachna and Anatis 

 it is not visible and no cases were seen of pigment disturbance. 



Pigment follows along the veins readily, especially along the linea ex- 

 terna, in cases of increase of pigment by modification; but in varieties of 

 spotted species of germinal constitution the influence of veins is not great. 

 The vittas w r hen present are frequently at an angle to the course of the 

 veins or broader upon one side of it than the other. Transverse confluence, 

 which is not influenced by any elytral structures, is more common than 

 vittae. 



There is pressure upon the elytron from below at the humeral spot by 

 the basal attachment of the wing below, at the site of spot e by a projec- 

 tion of the thoracic plates, at and near the site of spots 4 and 5 by the fold- 

 ing of the wings beneath, and at spot 6 by the tip of the abdomen when 

 bent back, as it frequently is. Nevertheless these spots are not infre- 

 quently absent and there is no especial pressure where other spots are 

 present. From these considerations and the well-known theoretical 

 objections to kinetogenetic origins of germinal characteristics, I am not 

 disposed to see any causal relation between pressure from below and the 

 position of the spots, although the coincidence is striking in the second 

 case. 



DEVELOPMENT OF PIGMENTED AREAS. 



The color-pattern of the head and thorax are fully formed at time of 

 emergence. The black pattern of the elytra is formed subsequently. The 

 soft, freshly expanded elytra are free from all black pigment. This is true 

 in all the species which I saw emerge, including Epilachna borealis, of 

 which the contrary has been stated. 



No sequence in the appearance of spots could be positively determined, 

 so nearly simultaneous is their development and so gradual is their appear- 

 ance. Where the pattern is composed of strongly confluent spots, the 

 pattern appeared at once, though not at first of full intensity, without pass- 

 ing through a separate spot stage. The pigment area, however, increased 

 slightly during the few successive days after emergence before the elytra 

 were fully hardened. This extension was so slight that it would not have 

 been detected but that the pattern of a few freshly-emerged beetles, the 

 pigment of which had become fully black, were described as having spots 

 1 and 3 very close together, but separate. Several days later they were 

 found to be slightly confluent. Confluence of this kind, however, is only 

 seen where the contiguous spots are unduly large and is the result of a 

 mere enlargement of spots. Their inheritance is like that of an extreme 

 fluctuant, as shown in pedigree table 15. Confluence, therefore, is of two 

 kinds. In confluence of the hereditary type, the spots may be quite small 

 and distant, as in Epilachna corrupta. 



