﻿COPEPODS FROM LAKE ERH HAI, CHINA — ^HSIAO 



195 



greater coefficient of variation. The females have longer carapaces 

 than the males — the difference between male and female carapace 

 lengths is 0.075 mm., which is ten times the standard error of the dif- 

 ference of the means. On the other hand, the ratios between the width 

 and length of the carapace in the two sexes are not significantly dif- 

 ferent. This agrees with the fact noted above that the females have 

 broader carapaces. In other words, the carapace is larger in the female 

 than in the male. 



5 6 7 8 9 



TOTAL LENGTH 



5 6 7 8 9 



TOTAL LENGTH 



Figure 29. — Carapace length-total length curves of Argulus japonicus from Erh Hai. 



On the average, the males have longer and wider abdomens than the 

 females — 0.16 mm. longer in this population. The width of the abdo- 

 men in the male is 71.3 percent of its length, while in the female it is 

 only 56.62 percent. As shown in table 6, the difference in the mean 

 values in both cases is significant. The presence of testes in the 

 abdomen makes that part of the body of the male not only longer and 

 broader but also thicker. 



The length of the anal sinus has been given by systematists as from 

 one-quarter to one-third the length of the abdomen. From this series 

 of material it is found that in the male the sinus is 37.755 percent of 

 the abdomen in length and in the female 38.435 percent. The other 

 data on abdominal sinus are listed below. 



Male Female 



Anal sinus, length, range 0.37-0.56 0.22-0.45 mm, 



length, mean 0.385 0.375 



length, standard deviation 0.047 0.053 



length, standard error of mean__. 0.001 0.001 



length, coefiBcient of variation 0.69 percent 0.88 percent 



Length of anal sinus 



— 37.755 percent 38.435 percent 



Length of abdomen 



Tokioka was the first person to report that in A. japonicits Thiele 

 the number of supporting ribs in the sucking disk is about 50. An 



