Manchester Memoirs, Vol. Ivii. (1913), A'c. 10. 5 



that the present case is certainly not of that character. 

 The primary conclusion of this enquiry, therefore, is that 

 the wide range of forms of Planorbis multiformis here 

 described all belong to a single species in the strictest 

 sense. 



Ontogeny : Variation in height with age. As already 

 explained, before the shells were classified according to 

 60- 



A 



Fig. 2. Curve similar to Fig. i, but with the com- 

 ponent individuals classified according 

 to size. 



Dotted line = individuals with base diameter 

 of o"o8-o'i2 inch. 



Broken line^^individuals with base diameter 

 (if oi2-o*20 inch. 



Coniinuous line = individuals with base dia- 

 meter of o-20-0'28 inch. 



height, they were divided into three groups according to 

 size. The curves obtained for each of the groups separately 

 are shown in Figs. 2 and 3. Fig. 3 differs from Fig. 2 

 only in the fact that the curves have been slightly smoothed 

 by summing the successive terms in overlapping pairs. 



For each set of shells we obtain a simple-variation 

 curve, thus confirming the conclusion from the general 



