570 GEORGE H. BISHOP 



mental conditions difficult to duplicate for animals undergoing 

 a less monotonous adolescence. 



Internally the bee is no less adapted to experimental investiga- 

 tion. Its response to a life of sequestered inaction has been a 

 repression or a rudimentary development of many of the larval 

 organs that would be required to adapt a larva to an active and 

 independent mode of life. Locomotor muscles, elaborate modi- 

 fications of the digestive system, complications of chitinous 

 hypodermis for protection or aggression, are little developed or 

 are lacking entirely. The larval life is given over to one function 

 predominantly — the storage of nutriment — and this stored-up 

 nutriment, as the fat-body, comprises at the time of metamorpho- 

 sis three-fourths of the body tissue (blood excepted) . 



After hatching, for five and a half days the chief activity of the 

 bee larva consists in the storage of food as fat-body tissue. 

 During the first four days of pupal existence this fat-body is 

 almost entirely histolyzed to furnish nutriment for the growth 

 of imaginal tissues. Hence, in the building up of this food into 

 fat-body cells, and the breaking down of these cells into tissue 

 nutriment again, one is justified in looking for a highly specialized 

 and, in a sense, an isolated process of nutritive metabolism. 



2. Histology of the fat-body 



Histogenesis. The fat-body in insects is a tissue of mesodermal 

 origin, the cells of which originate in the embryo by division and 

 segregation from the inner surface of the mesodermal tubes 

 along what is destined to be the ventrolateral aspect of the body- 

 space. These cells form a mass of tissue running along the body 

 between the intestine and the ventral body wall, attached to 

 each. Typically, during embryonic or early larval life, the cells 

 multiply to the full number to which the larval fat-bodj- will 

 attain. Thereafter, the growth of this tissue consists in enlarge- 

 ment of its cells, and not in their numerical increase. The bulk 

 of the tissue relative to the size of the body varies in larvae of 

 different insects from a narrow band on either side of the nerve 

 chain in the embryonic position to a massive growth which 

 comprises the greater part of the bulk of the larva. In the bee 



