126 PROCEEDINGS OF THE ACADEMY OF [Jan., 



THE DEVELOPMENT AND COMPARATIVE STRUCTURE OF THE GIZZARD 

 IN THE ODONATA ZYGOPTERA. 



BY HELEN T. HIGGINS. 



The following study^ was undertaken on the advice and under 

 the direction of Dr. Philip P. Calvert, instructor in Zoology in the 

 University of Pennsylvania. 



Dr. Ris' work on the gizzard of the Odonata and Dr. Calvert's 

 study of Californian forms strongly suggested the phylogenetic 

 importance of this organ. 



The present study has been limited to the more primitive 

 Odonata — the suborder Zygojjtera. 



I am indebted to Dr. Calvert for the material placed at my dis- 

 posal, for many of my preparations, including his slides used in 

 his paper of 1899 mentioned later, for the determination of genus 

 and species in every case, and for the suggestion of the structural 

 formula used in describing the gizzards. 



In 1890, Dr. F. Ris published" a paper entitled Untersuchungen 

 ' iiber die Gestalt des Kaumagens bei den Lihellen and ihren Larven. 



The results of his investigations are briefly outlined here: 



In the Odonata the fore-gut extends to the third abdominal seg- 

 ment. In larva and imago alike the gizzard is found at the pos- 

 terior end of the fore-gut in the second abdominal segment. It is 

 formed by a thickening of the muscle layer, and by a modification 

 of the chitinous coat of the fore-gut to form folds armed with 

 teeth. The number of these folds is four, eight or sixteen. The 

 metamorphosis to the imago shows a regular reduction in the 

 strength and complication of the elements, but their number varies 

 greatly. At the metamorphosis, the larval lining is shed with the 

 chitinous coat of the exterior of the body; Dr. Ris states that he 

 found in a Lihellula, directly after metamorphosis, the old gizzard 

 lining enclosed within the new. He examined the larval and adult 



^ Accepted by the Uliiversity of Pennsylvania as a thesis for the degree of 

 Bachelor of Science in Biology, June, 1900. 

 ^ Zoolog. Ja/trbiicJt., IX. 



