to the same low level as in the operated flies. Therefore the values are calculat- 

 ed per individual midgut. 



Egg-chambers of flies — m. n. с have never been found to exceed 0"17 mm 

 in length, therefore the size of the ovaries was used as a control of the operation. 

 The developmental stage of the ovaries of the other categories of flies was 

 also noted. 



Table 1 shows the result of the second series of experiments. 



Let us first regard the normal flies, and begin with the 7 — 9 hours old fhes, 

 i. e. flies having the same age as the operated flies when the operation is per- 

 formed. The proteinase activity of these flies is very low, vayring from 0-1 — 1-0 

 with an average of 0-5. 



In flies fed for 5 days on sugar and water only, the proteinase activity 

 is on an average 0-8 with a variation from 0-3 — 1-6. This figure is a little 

 higher than that of the young flies but most probably the difference is not 

 significant. 



If we now turn to the normal controls which were fed on sugar and water 

 and meat, it is obvious that these fall into two groups according to the develop- 

 mental stage of their ovaries. One group with developing ovaries has a protein- 

 ase activity varying from 4-9. — 26-1, the average being 13-6, and the other 

 with mature ovaries has a proteinase activity from 1-0 — 3-9 with 2-1 as an 

 average. We will leave the second group out for the moment. 



Thus the proteinase activity of the sugarflies is on an average only 6% 

 of that of the flies with developing ovaries which were given meat as weU 

 as sugar and water. This shows clearly that in order to be able to produce 

 a fair amount of proteinase, Calliphora must eat meat. 



If we now regard the females deprived of their m. n. c, the midguts of these 

 display a proteinase activity which varies from 1-6 — 9-5 with an average 

 of 3-3. It should be mentioned that the midguts of all these flies contained 

 meat, — and so far we have found no indication that the flies — m. n. с 

 eat less meat than the controls. Thus the difference between the proteinase 

 activity of fhes — m. n. с and that of normal flies is striking, the former 

 having only at the most 25% of the amount found in normal females with 

 developing ovaries. This figure drops to 19% if we disregard the exceptional 

 high value, found in one of the females — m. n. с Therefore it can be concluded 

 that in the absence of the neurohormone from the m. n. с the gut cells are 

 only able to produce a small amount of proteinase. 



As the midguts of the flies contained meat the figures do not merely give 

 the values of the proteinase activity of the intestine itself, but also the activity 

 of the intracellular proteinases of the meat, but whatever its size it should 

 be the same in all the flies fed on meat. 



The proteinase activity of the females — ra. n. с is about 4 times that 



124 



