HISTOLYSIS OF FAT-BODY OF APIS o73 



There are no trachea extending into the laminae. In the deeper 

 layers are embedded the malpighian tubules and the saUvary 

 and spinning glands. The hind-intestine, unlike the mid- 

 intestine, is entirely enveloped. 



3. Relation to larval activity 



This tissue occupies a space so prominent and so extensive in 

 the larval anatomy and forms so large a proportion of its mass 

 that the larva seems to be merely a mechanism for nourishing 

 the fat-body, rather than the fat-body an organ of the larva. 

 This illusion is supported by the low degree of development of 

 any organs not concerned with the assimilation of food; i.e., the 

 fat-body itself, the digestive apparatus, including the salivary and 

 spinning glands, and the excretory system. The physiological 

 assimilation of most of the food the larva takes goes on in the 

 fat-body, the functional unit of which is the individual fat-cell. 



As in all the Hymenoptera, the metamorphosis is complete. 

 It involves the destruction of all the typically larval organs and 

 the formation of a full set of imaginal tissues. This degenerate 

 and highly specialized larva, consisting of a living sac full of 

 stored-up nutriment, thus transforms into one.of the most elabo- 

 rately and highly specialized of mature insects. The transfor- 

 mation is so extreme and so abrupt that it demands the inter- 

 ruption of even such activity as the bee larva exhibits, and the 

 pupal stage is entirely inert. 



Nutrition and metamorphosis 



The fat-body of the bee, compensating as it does for the large 

 masses of muscle, etc., developed by more active larvae, is also 

 presumably a more efficient mechanism for food storage, by 

 leason of its high fat content, than the usual larval tissue. The 

 histolysis during larval metamorphosis, therefore, is to be con- 

 sidered as more than a mere removal of a no longer useful larval 

 organ ; an intracellular digestion goes on by which a large amount 

 of reserve tissue nutriment is elaborated with very little waste. 

 Its cells may be interpreted as having two methods of functioning, 



