474 



Geoffrey Smith 



Table 1. 



Frequency distribution per cent of Sizes in Male G. maxillaris. 



12 3 4 5 6 7 8 



70 

 65 

 60 

 55 

 50 

 45 

 40 

 35 

 30 

 25 

 20 

 15 

 10 



12 3 4 5 6 7 8 



Scale of measurement in millimeters. 



It will be seeu from this curve that the modal or most freciuent 

 size is 2 mm, but a eloser iuspection of the curve shows that it is 

 not at all normal in its shape, being decidedly skew in the direction 

 of the larger measurements with the tendency to establish another 

 mode at 5 mm. Out of the 465 males examined only 12 measured 

 4 mm while 43 measured 5 and 1 5 measured (i mm i. Now it is a most 

 reinarkable fact that out of 29 g-iaut segmeuted larvae 26 measured 

 ai)i)roximately between 4 and 5 mm. Putting these facts together it 

 appears that thcre are two chief criticai periods at v\^hich the male 

 (and i)robably also the female) Praniza metamorphoses into the adult: 

 firstly wlien it has attained to about 2 mm and secoudly when it 

 has attained to about 5 mm. If it is brushed off its host when it 

 measures between 4 and 5 min it cannot assume the adult state but 

 undergoes retrogressive metamorphosis into the giant segmented 

 larvae which must become attached to a lish again and go on 

 growing before arriving at sexual maturity. By this hypothesis only 

 do we obtain an explanation of the bimodality of the frequency 

 curve of sizes and of the occurreuce of giant segmented larvae which 



' The most probable error of the frequency at 4 mm is =t 2,306. 



