56 THE UNIVERSITY OF OKLAHOMA 



assume a new and fascinating .interest in the march of science 

 toward an uhimate goal of exact knowledge. 



VII. UNILATERAL INHERITANCE IN BRUCHUS 



J. K. Breitenbecher 



From the Zoolcgical Laboratory of the University of Oklahoma. 



Contribution No. 33, Second Series. 



Any person who has observed living things knows that there 

 exists in nearh' every animal as well as in man a harmonious rela- 

 tion of functions due to a -ditplication of structures. Almost every 

 animal manifests symmetry and nearly all are bilaterally symmetri- 

 cal with the exception of Echinoderms which show a radical type 

 adapted from a bilateral. Bilateral symmetrv is found in all verte- 

 brates and nearly all invertebrates. Often, "however, one discovers 

 a few organs which are asymmetrical such as the heart, pancreas, 

 etc., i. e., all organs do not manifest symmetry. 



In Bruchns, the insect which we use for our studies, bilateral 

 symmetry is manifested by duplication of appendages, wings, and 

 other structure, as well as spots, patterns, and colors. Bruchns has 

 two black spots bilaterally located on each elytrum. From this 

 culture there appeared on October 23, 1922, an abnormal female 

 insect having a right elytrum red spotted, intead of the usual black 

 spots. The first thought was that this unilateral character was 

 a mosaic and due to a somatic mutation. But the offspring from 

 this mosaic proved that the character was inherited, and it is 

 the object of this paper to discuss briefly the problem concerned. 



Symmetry has always been a question for scientific debate. 

 Prof. Child whose idol is the "axial gradient theory" maintains 

 that symmetry is determined by differences in metabolic rates. 

 That region of the reproductive cell or part of an organism having 

 the highest rate of metabolism becomes the animal pole. As this 

 rate decreases posterially development continues in that direction 

 until polarity is determined. He believes that differences in a 

 metabolic gradient toward the periphery causes bilaterality. In 

 contrast to this idea nearly all embryologists interpret polarity as 

 being pre-shadowed in the cytoplasm of the egg previous to fertil- 

 ization. This is no doubt true for Br-uchus since all insects mani- 

 fest polarity while the eggs are still in the ovary. 



In the frog, as in all animals, bilateral symmetry appears soon 

 after fertilization. Certain animals, especially snails, show a re- 

 version from the normal type of symmetry. In Bruchus we also 

 discover that the asymmetrical trait under our observation may 

 be the reverse from normal due possibly to a different mutation. 



