298 Insect and other Invertebrate Fauna 



some cases even greater. The same relation existed again between the 

 fifth and fourth layers. The fact that the figures given above do not 

 coincide with this is due chiefly to the distribution of the ants, which 

 occurred on two occasions in large numbers, owing to the sample con- 

 taining part of a nest. One of these nests occurred in the first layer of a 

 sample from the manured plot, and the other in the third layer of a 

 sample from the control plot, before the plots were ploughed. 



In Fig. 7 the Formicidae have been omitted. This diagram indicates 

 very clearly that the Insecta, ^' Myriapoda'^ and Oligochaeta (Terricolae) 

 probably penetrate to a greater depth than nine inches. 



A few groups showed noticeable variations from the above general 

 rule. The Acarina, Cecidomyidae (larvae), Chironomidae (larvae) and 

 Trichocera (larvae) were found to occur in much larger proportions in 

 the upper layer than in the second, and very few occurred below the five- 

 inch level. With the Symphyla the usual proportions per layer were 

 practically reversed, much the greatest proportion of this group occurring 

 in the fourth and fifth layers. 



After the plots had been ploughed the effect of the ploughing on some 

 of the groups of invertebrates was very clear for some time. Taking the 

 numbers of Collemhola for example, from the beginning of the investiga- 

 tion in February to the time of ploughing in October, the percentages 

 in the five layers were: I 29-0; II 44-0; III 19-8; IV 3-0; V 4-1 in the 

 manured plot, and I 28-6; II 46-8; III 16-1; IV 4-6; V 3-6 in the control 

 plot. 



For the period from the time of ploughing to the end of the investiga- 

 tion, the percentages were: I 2-1; II 12-2; III 20-1; IV 44-6; V 20-9 in 

 the manured plot, and I 14-3; II 14-3; III 28-6; IV 28-6; V 14-3 in the 

 control plot. 



In the case of the Elateridae larvae, taking the whole period of the 

 investigation, the percentages at the different depths were, in the manured 

 plot: I 1-7; II 18-6; III 20-3; IV 32-2; V 27-1; and in the control plot: 



I 12-2; II 18-4; III 26-5; IV 32-6; V 10-2. Taking only the period from 

 the commencement of the investigation to the time of ploughing the 

 percentages at the different depths were, for the manured plot: I 2-8; 



II 30-5; III 27-8; IV 22-2; V 16-7; and for the control plot: I 11-6; 

 II 20-9; III 27-9; IV 34-9; V 4-7. After the plots had been ploughed, 

 taking the period from the time of ploughing to the end of the investiga- 

 tion, the percentages at the different depths were, for the manured plot: 



I nil; II nil; III 8-7; IV 47-8; V 43-5; and for the control plot: I 16-7; 



II nil; III 16-7; IV 16-7; V 50-0. 



