462 



crystals within them, and he regarded the fat-body as an 

 excretory organ. 



In 1908 K. Samson observed that in the moth Hetero- 

 genea the fat cells stored up vast quantities of urates during 

 metamorphosis. The fact seems, then, to be fairly well estab- 

 lished that the fat-body is in some way concerned with ex- 

 cretion ; but whether it is a depositing place for urates, found 

 elsewhere in the body, or whether the urates within it are 

 the result of its own deaminising activity, these observations 

 do not allow one to decide. 



In Nasonia crystals are present during late larval life, 

 and a considerable portion of the pupal period, and they dis- 

 appear as the urate crystals begin to accumulate within the 

 intestine. Similar crystals are often seen in the nucleoli of 

 degenerating larval cells, and it is possible that their presence 

 within the fat cells is only secondary, their seat of origin 

 being within the active tissue cells. In the larva of Nasonia, 

 as already pointed out, excretory organs are absent, and unless 

 nitrogen is liberated as ammonia, no removal of excretory 

 products takes place. 



Recently (1920) Perez has shown that during meta- 

 morphosis there is no evacuation of urates by the malpighian 

 tubes until towards the end of pupal life. Then there is a 

 sudden accumulation of urates within the intestine (just as 

 occurs in Nasonia), and this coincides with a disappearance 

 of the pseudonuclei from the fat-body. He regards the fat- 

 body, therefore, as an ''accumulating kidney." 



These various investigations seem to show that the fat- 

 body may remove urates from the blood during the meta- 

 morphosis, and should be especially useful in such an insect 

 as Nasonia, where the removal of nitrogen during larval life 

 does not seem to occur. 



The fat-body has besides another great function — that of 

 storing reserve materials. These are mainly in the form of 

 fat globules and of the numerous grains which are so char- 

 acteristic of the tissue. The latter are usually regarded, 

 though without any direct chemical evidence, as protein in 

 nature. 



It is this capacity of storing food materials that is so 

 important in insect metabolism, and it is largely this that 

 has enabled the insect metamorphosis to be evolved. 



THE GONADS. 



The Male Organs. 

 The testes are present in the earliest larva as a pair of 

 large pyriform structures, situated on either side of the 



