MUSCULAR REORGANIZATION IN THE ODONATA DURING METAMORPHOSIS. ARTHUR D. WHEDON, DEPARTMENT OF ZOOLOGY, NORTH DAKOTA AGRICULTURAL COLLEGE. INTRODUCTION. Extensive investigations have been made into tissue reorganiza-tion in the Holometabola, especially the Lepidoptera, Diptera and Hymenoptera. The profound nature of these changes has prob-ably overshadowed the less extensive ones which might be seen in the Hemimetabola. At least, no study has been devoted to the latter. Indeed, so little is known of the Neuropteroid and Orthop-teroid insects in this respect, and perhaps so much inferred from the Holometabola, that a gross misconception has persisted al-most to the present regarding even the period in the life cycle of such an insect when tissue reorganization is accomplished, to say nothing of uncertainty as to the nature of the metabolic proc-esses responsible for the changes. The Odonata, perhaps typical of those forms which pass rather suddenly from aquatic larva to aerial imago, is a good example. In his "Biology of Dragonflies," Tillyard (1917) states that " The emergence of the imago from the larval skin or exuviae, usually spoken of as metamorphosis, is in point of fact only the consummation of an internal metamorphosis which begins a con-siderable time before. The beginning of this change is marked by an alteration in the color and behavior of the larva. The color darkens considerably, greenish larvae becoming a dull opaque brown. The larva becomes listless and refuses to feed. Rapid proliferation of the hypodermal cells, preparatory to the forma-tion of the imaginal exoskeleton, causes the larva to appear tense and swollen." The changes in the eyes and other parts are then mentioned but nothing is said of the retraction of the labium, which begins at the time the insect ceases to feed, or of the de-generation of the gills within the rectum and of the opening of 177
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