ACHERONTIA ATROPOS AND SPHINX CONVOLVVLI. 281 



the point where this line meets the curve a vertical line is drawn to 

 the scale recording the number of spots. The point where the line 

 meets the scale is the mean (M). This mean, so calculated, has several 

 properties : when the curve is symmetrically disposed on either side of 

 it, it is equal to the arithmetical mean, and this is the case with the 

 curves given here, so that the figures 4^ and 7 might have been obtained 

 by the ordinary method of averaging ; but I determined to throw the 

 figures into the form of a scheme, as this method will be of advantage 

 later on. Although curves A and B are normal with respect to their 

 M, they are not normal in general slope. Curve C is an example of a 

 curve normal in slope and in all respects. The bearing of these dif- 

 ferent kinds of curves on the subject will be seen in the sequel, 



(To be continued.) 



ACHERONTIA ATROPOS AND SPHINX CONVOLVULI IN 

 THE HARWICH DISTRICT. 



By Fleet Paymaster Gervase F. Mathew, R.N., F.L.S., F.E.S. 



On August 14th a labourer brought me a fine larva of 

 A. atropos and said that he found it under a bush while he was 

 looking for mushrooms. This I doubted, but it showed me that 

 the larviTB were already full grown, and as I wanted to breed a 

 few to renew my old series, I paid a visit the following afternoon 

 to a potato-field not far from my bouse, and, after a couple of 

 hours' search, succeeded in finding seven, nearly all full grown. 

 They were magnificent creatures, all bright golden green with 

 the usual oblique blue stripes and dots. They were not difficult 

 to find, for by walking slowly between the rows of potatoes one 

 could see where the larva had been feeding, as the haulms in 

 many instances were nearly stripped, and if the larva had not 

 buried it w^as usually to be found upon the under side of one of 

 the lower leaves. I found many plants so eaten by larvte that 

 had already gone down, which shows that they have been 

 numerous and early this season. Where the plants were not of 

 luxurious growth the larva was easy to see some distance off, and 

 one fine fellow I detected nearly a hundred yards away, as it 

 rested on a bare stem, where it looked very conspicuous in the 

 rays of the setting sun. 



My children were very much excited at my capture of these 

 huge caterpillars, and the next morning, the 16th, four of them 

 set out at 6 o'clock to look for more. When they came home to 

 breakfast they said they had found three, but that they were 

 smaller than mine, and two of them were green, and the third 

 nearly black, and their horns were smooth ; so, after breakfast, 

 I went out into the garden to have a look at them, and directly 

 I saw the first, which they took out of the large breeding-cage in 



