NO. 7 MUSCULATURE OF COLEOPTERA — ^DORSEY 3 



In order to observe carefully the places of origin and insertion of 

 the labral, labial, hypopharyngeal, and pharyngeal muscles it is neces- 

 sary to remove the maxillae and mandibles and their muscles. The 

 maxillary, mandibular, and antennal muscles are not included in this 

 study. 



This particular work evolved from an interest as to how chewing 

 insects actually accomplish the feat of getting the food into the true 

 mouth, which, of course, is located in the posterior region of the 

 cibarium. Much is known as to how these insects procure and chew 

 their food, but the hypopharynx though tonguelike in position could 

 not be very efficient in accomplishing the work done by the tongue of 

 a vertebrate. In many insects the hypopharynx, for all practical pur- 

 poses, can be considered to be absent ; such insects also ingest food 

 and thrive, so the hypopharynx alone cannot be responsible for the 

 act of placing the food in the mouth from which point it can be 

 swallowed. 



It is difficult and often impossible to identify corresponding muscles 

 on a functional basis. A muscle, for example, as found in one species 

 may be an adductor while its homolog in another species is perhaps 

 a retractor because of some slight change in the position of the point 

 of insertion. For this reason the general application of functional 

 names to insect muscles is limited ; a careful study of each species 

 individually is necessary to ascertain muscle functions. 



It is hoped that the facts of the arrangement of muscles, and cer- 

 tain anatomical observations herein presented will contribute to a 

 better understanding of the means of ingestion of food by chewing 

 insects, and also of the homologies of muscles between orders of 

 insects, or between families within an order. 



The Leng system of classification as modified by Boving and 

 Craighead (1930) is followed, and at least one family from each 

 superfamily selected from which a genus is chosen for study. When 

 possible the immature stage of the same genus is used. The species 

 of Coleoptera included in this study are not considered as representa- 

 tive, necessarily, of their respective families. 



This work is presented in partial fulfillment of the requirements 

 for the degree of Doctor of Philosophy in the Graduate School, 

 Entomology Department, University of Maryland. The study was 

 carried on under the direct supervision of R. E. Snodgrass of the 

 United States Department of Agriculture, Bureau of Entomology 

 and Plant Quarantine, who is also a member of the staff of the Uni- 

 versity of Maryland, Entomology Department. The writer is sin- 

 cerely grateful to Mr. Snodgrass for his guidance and encourage- 



