ENTOMOLOGY 



abdomen from tissues that can scarcely be distinguished from fat- 

 tissues. The corpuscles (leucocytes, or phagocytes) which in some insects 

 absorb effete larval tissues during metamorphosis have been by some 

 authors regarded as wandering fat-cells. Cells constituting the peri- 



cardial fat-body are attached to the 

 lateral muscles (alary muscles) of the 

 dorsal vessel, but almost nothing is 

 definitely known as to their function. 

 CEnocytes. Associated with the 

 fat-body proper and with tracheae as 

 well are the peculiar yellow cells known 

 as oenocytes (Fig. 168), that occur in 

 abdominal segments of larvae. These 

 cells are enormous in size as compared 

 with all other insect-cells excepting ova, 

 and are essentially isolated from one 

 FIG. 167. Section through fat-body of a another, though grouped among tra- 

 siikworm, showing nucleated cells, loaded cne al branches i nto loose clusters, one on 



with drops of fat. 



each side of a spiracle-bearing segment. 



After arising from the primitive ectoderm the oenocytes never divide, 

 but gradually increase in size (Wheeler), and their size is in a general way 

 proportional to that of the fat-body. 



Their function has been problematical until recently. Many ob- 

 servers have regarded them as ductless glands, having seen " microscop- 

 ical exudations around the periphery of the cytoplasm, 

 especially at times when the nucleus is greatly rami-' 

 fied, and therefore manifesting its great activity" 

 (Glaser). 



R. W. Glaser has thrown light upon the nature of 

 the cenocy tic fluid. By using three-year-old caterpillars 

 of the leopard moth, Zeuzera pyrina, which have a 

 great amount of fatty tissue and correspondingly large 

 oenocytes, he was able to extract enough of the fluid 

 for chemical experiments. He found by carefully con- 



J J cytes and accom- 



ducted tests that the fluid had the power of oxidizing panying tracheae, 



fats, by means of enzymes known as oxidases (though s in^orm. r 



no fat-splitting enzyme, or lipase, was present), and 



concluded that the secretion of the ceixocytes is used to oxidize the 



reserve food stored up by the larva in the form of fat. 



Photogeny. This phenomenon appears sporadically and by various 

 means in protozoans, worms, insects, fishes and other animals. Lumi- 



