12 VICTOR E. SHELFORD. 



tion on the part of the female during tin- breeding reason or 

 striking elimination of all eggs laid in tin- ponds in which the 

 larvae are not found. 



It is evident that ecological types (here represented by the 

 various species) succeed each other as the ponds change with age. 

 Succession is here as elsewhere, a succession of all, or at least a 

 majority of the animals present. 



(b) Quantitative Comparison. (i) Vegetation. Vegetation 

 is evidently a good index of the content, or the relative numbers 

 of the different species of plants and animals. In Table I., page 

 3, we note that more than two thirds of the bottom of pond I 

 is covered with humus. Vegetation covers about 70 per cent, 

 of the area. In pond 5r vegetation covers about 95 per cent, 

 and in 7 a about 99 per cent, of the area and in 146 100 per cent. 

 If the plants of each unit area were equal in volume, these per- 

 centages would represent relative volume also. More of the 

 plants of the older ponds reach to the surface; plants are closer 

 together in the older ponds. It is obvious from inspection that 

 the volume per unit area is greater in the older ponds. 



A single test was made with a large tow net. The net was 

 drawn a distance of 40 feet in three of the ponds and the volume 

 of vegetation torn off by the net was measured by displacement 

 and reduced to terms of 100. This would give relative volume 

 if all plants were torn with equal ease. 



Finally Mr. G. D. Fuller and myself have made an estimate 

 based on several inspections. 



TABLE XV. 



SHOWING MEASUREMENTS AND ESTIMATES OF RELATIVE VM \n OF \ i DICTA- 

 TION PER CUBIC UNIT. 



(2) Plant and Animal Food. The plant and animal tood in 

 solution is expressed in a general way by the sanitary analysis. 

 The results of a single analysis with the total carbonaies added, 

 arc given in Table XVI. 



