1909.] NATURAL SCIENCES OF PHILADELPHIA. 3 



A CONTKIBUTION TO THE COMPARATIVE MORPHOLOGY OF THE THORACIC 



SCLERITES OF INSECTS. 



BY G. C. CRAMPTON, PH.D. 



Although the thoracic sclerites are much used factors in insect 

 classification and myology, there exists a most confusing lack of 

 uniformity in the homologizing and terminology employed by the 

 various writers upon these subjects. This confusion, it would appear 

 has largely arisen from the fact that each investigator has been con- 

 tent to confine his attention to one or two groups of insects, applying 

 his own terminology as occasion arose, or, more frequently, naming 

 the sclerites without sufficient comparison with intermediate forms 

 to determine their true homologies. 



As would be naturally expected, many new and important points 

 have been brought to light in each of the orders, but they stand as 

 isolated facts, rather than as generalities applying to the Hexapoda 

 as a whole. It is with the purpose of applying this knowledge to 

 insects in general that a comparative morphological study has been 

 here attempted. 



Material. 



The insects for study were collected in the United States, Europe 

 and North Africa. With these I was able, through the kindness of 

 Prof. R. Heymons, to compare a number of rare specimens in the 

 Berlin Museum, not otherwise accessible. However, in so far as was 

 possible, the commonest insects have been chosen to illustrate the 

 types discussed, in order that any one wishing to verify the results 

 might have no difficulty in procuring the necessary material. 



Technique. 



The binocular microscope was found indispensable to the perform- 

 ing of dissections, which were always made and studied under a 

 liquid medium, the rays of an artificial light being concentrated upon 

 the object by means of a bull's-eye condenser. Glycerine or oil proved 

 to be the most favorable medium for the examining of small objects, 

 since they more readily remain in the position in which they are placed , 

 when a denser medium is used. 



