OF ARTS AND SCIENCES, 255 



doptera: " Although we do not know the steps by which these wonder- 

 fully beautiful and complex ornaments have been developed the 

 process, at least with insects, has probably been a simple one ; for, as 

 Mr. Trimen writes to me, no characters of mere marking or colora- 

 tion are so unstable in the Lepidoptera as the ocelli, both in number 

 and size." 



As far as I know there is nothing more published on this subject. 

 In some few instances I have been able to observe how the pattern is 

 produced. In dragon-flies (Odonata) the thorax is transparent and 

 entirely colorless at the moment of transformation. At this time the 

 muscles are in process of formation. The thoracic muscles of the 

 Odonata are, as is well known, very powerful, and rather exceptional 

 in the shape of their tendons. I observed very strong currents of the 

 blood just along the place where the muscles were developing. The 

 rush of the blood was very much accelerated. Now just outside of 

 these we find in Odonata dark lines or bands, which appear to be the 

 result of the formation of the muscles. Ubi irritatio^ Hi affluxus ; 

 therefore it is not improper to conclude that a powerful action in the 

 development of the muscles is here the cause of a stronger combus- 

 tion and of an oxidation in the adjacent parts of the external crust 

 of insects. But not the pattern of the thorax alone follows the 

 lines of the muscles. On the head we find a certain pattern corre- 

 sponding to the muscles of the mandibular apparatus ; another one on 

 the segments of the abdomen corresponding to the so-called respira- 

 tory or abdominal muscles, and another one on the legs corresjDond- 

 ing to their muscles. It is important to remember that those patterns 

 are better and more definitely developed in the most powerful flying 

 Odonata, as in the ^schnina, and especially in the Gomphina. The 

 main color of the Gomphina is yellow of different shades, mostly 

 greenish-yellow, and the stronger the species the larger is mostly the 

 pattern of blackish bands. 



I have observed the same proceedings in Cicada just emerging from 

 the nympha skin. On the head, thorax, abdomen, and legs appear 

 similar patterns, corresponding to the muscles or to their insertion 

 places. In fact where a stronger circulation exists in insects, the 

 parts become more strongly chitinized and darker colored. 



Should my explanation of these facts be accepted, we shall have 

 taken a step forward in understanding the origin of the pattern. I 

 know very well that among the Odonata patterns exist which do not 

 agree with my explanation, and in one case are even opposed to it. 



