HISTOLYSIS OF FAT-BODY OF APIS 569 



tissue seems well adapted for this. The present paper aims to 

 lay down the anatomical basis for such a series of experiments. 

 In part I the role of the fat-body is defined in relation to general 

 larval activity, and the structure of its cells as functional ele- 

 ments is described and in part II is discussed the functional sig- 

 nificance of these cell elements in metabolism. 



Acknowledgments are due especially to Dr. M. F. Guyer, 

 of the University of Wisconsin zoological laboratories, for much 

 valuable advice, and to Dr. Wm. S. Marshall, of the same 

 institution, for literature references and suggestions as to insect 

 metabolism. 



THE ROLE OF THE FAT-BODY IN LARVAL METABOLISM 



1. Larval development 



The larvae of the honey-bee are available in quantities and 

 lend themselves readily to investigation. From the laying of 

 the egg to emergence of the imago, a larva passes its existence 

 in a cell approximately 4 mm. across by 9 deep. For the first 

 part of its life it is half immersed in the partially digested food 

 administered to it, the food being later disgorged by the worker 

 bees directly into its mouth. It lies in the position in which it 

 was first hatched until the confines of the cell containing it 

 compress its flabby bulk into a flattened ring, whereupon it 

 straightens itself out and spins a cocoon. The larva then pupates 

 and is quiescent until it quickens as a mature insect. 



From the standpoint of metabolism, the bee larva approaches 

 what might be called a closed system. During a developmental 

 period of twenty-one days it passes no excreta. The content 

 of the malpighian tubules and a few faeces collect in the hind 

 intestine, which, however, does not make functional connection 

 with the stomach until late in development ; the stomach contents 

 are regurgitated at the beginning of pupation. The food taken 

 in is of determinable and relatively unvarying composition. The 

 developmental period is definite in time, and the temperature of 

 the bee cluster is maintained with remarkable constancy. Thus 

 the natural environment of the larva furnishes controlled experi- 



