﻿196 PROCEEDINGS OF THE NATIONAL MUSEUM vol. lOo 



examination of a random sample of this species from Erh Hai shows 

 that the number of supporting ribs varies from 38 to 50, with 44^5 

 (44.6) as the mean. It also shows that the two sucking disks of the 

 same animal do not have the same number of ribs. A random count- 

 ing is shown below : 



Number of supporting ribs in sucking disk 



Right side 43 43 45 46 43 48 45 42 43 39 45 45 



Left side 46 45 48 43 45 45 50 44 41 38 47 50 



In the foregoing discussion on the length of the carapace and the 

 abdomen, only animals larger than 3.5 mm. are used for comparison. 

 But when the young and old are examined together, or when the 

 young ones are compared by themselves, it is found that the carapace 

 does not grow isauxetically in length with reference to the total 

 length of the animal. As the length of the carapace has been used in 

 describing argulids — how far its posterior border reaches, to the 

 abdomen or to the third or fourth leg, etc. — a comparison of the rel- 

 ative length of the carapace is made. In figure 29 the mean length 

 of the carapace has been plotted against total length on a double log. 

 grid for the larger animals. The line with slope =1 shows very well 

 the trend of all the points for both males and females. But in the 

 case of animals less than 3.5 mm. long, as shown in figure 30, B, the 

 slope of the line of best fit drawn by sight is 0.957. In other words, K 

 is less than 1, which means that the anteroposterior length of the cara- 

 pace shows brachyauxesis though its width shows isauxesis with refer- 

 ence to total length. In the very young specimens in this collection the 

 posterior border of the carapace reaches only the anterior edge of the 

 second leg, while in larger ones, it reaches the base of the fourth. 



In the case of the abdomen, as shown in figure 30, A, the points re- 

 lating abdomen and total lengths in animals less than 3,5 mm. long 

 seem to fall along a line with ^=^1.65; in larger animals along the 

 line with K=l. In this figure the dots represent larger animals, and 

 the crosses, whose trend is indicated by the broken line, are based on 

 animals smaller than 3.5 mm. in total length. This means that during 

 rapid growth the abdomen increases in length tachyauxetically with 

 reference to the rest of the body, but after maturity, or near maturity, 

 it shows isauxesis. 



With the above statistical data a slightly different description, more 

 useful for comparative purposes, might be given as follows : 



Adult female : Carapace nearly circular, width 92 ± 1.05 percent ^ 

 of carapace length, carapace length 64.92 ±0.23 percent of total length, 

 nearly reaching anterior margin of fourth swimming leg, parts of 



' Figure after ± sign represents standard error of mean. Tliis applies to all the figures 

 used in this description. 



