1892.] Correlated Variations tn>Cratigon vulgaris. 5 



Figs. 2 and 3. — Curves of frequency of all observed magnitudes of post-spinous 

 lengths (fig. 2) and total carapace lengths (fig. 3) in 1000 adult female shrimps 

 from Plymouth. The dotted curve is a probability curve of the calculated probable 

 error : the continuous curve shows the results of observation. The horizontal scale 

 represents thousandths of the body length : the vertical scale represents tens of 

 individuals. 



the value of r can be separately determined. This process has been 

 performed for each of the values entered in the first two columns of 

 Table I, and the results are recorded in the third and fourth columns. 



In Table II, the results of a similar process are shown, but the 

 individuals have been sorted into groups in each of which the length 

 of the post-spinous portion of the carapace is constant, and the mean 

 value of the total carapace length has been determined in each group. 

 As before, the immediate results of these determinations are entered 

 in the first two columns, and the deviation of each entry in these 

 columns from its corresponding average, divided by its "probable 

 error," is given in the third and fourth columns. 



