20 COLORATION. 



the neotropical region, where two forms of coloration, 

 rare in Europe, are very common, there being scarcely 

 a genus without an example of the two patterns. In 

 one case the body and wings are black, or bluish-black, 

 and the prothorax and, it may be, part of the meso- 

 notum, red ; in the other the ground colour is yellow 

 with black on part of the thorax, and the wings yellow, 

 with two or more broad black bands. Of the first 

 class we have two or three British examples, of which 

 Blennocampa eppiphium is the best known. As the 

 insects having this form are broad compared to their 

 length, and as they have the habit of folding the wings 

 and of pressing the antennge and legs close to the body, 

 and dropping to the ground, where they remain motion- 

 less as if dead, it is possible that the red on thorax may 

 aid in concealing them. The other type of coloration is 

 a common one with terebrant Hymenoptera in South 

 and Central America, and I suspect it has some refer- 

 ence to the flower-frequenting habits of the insects. 



Secondary Sexual Characters. 



Apart from the internal or primary sexual characters, 

 there are more or less well-marked secondary distinc- 

 tions between the males and females. These differ- 

 ences may be grouped under six heads, it being 

 premised that in all cases the males are smaller, and 

 of a slighter build than the females, while the abdomen 

 is flat, seldom or never cylindrical. 



1. Coloration. The general rule is that the males 

 are darker and more obscurely coloured than the 

 opposite sex, while their specific characters are much 

 less well marked. In many luteous species of Nematus, 

 for example, the males have the upper surface of the 

 body black ; in others, e.g. Macrophya, they want the 

 white, yellow, or reddish markings, which the 

 females have on the legs, thorax and abdomen. Many 

 species show no distinction in colour between the 1 

 sexes, while in others it is extreme. Thus with 



