﻿140 Proceedings of the Royal Physical Society. 



that 82, or 6*6 per cent., of these 1249 specimens were 

 abnormal as regards their genital apertures. In addition, 

 205, or 6"3 per cent., abnormal males were found among the 

 remaining 3180 examined. This gives a total abnormality 

 of genital openings amounting altogether to almost 6*5 per 

 cent., or 287 out of 4429 specimens. This percentage, 

 though not so high as Dr Marshall found in 19U1, is 

 sufficiently high to be worthy of note. It may be recalled 

 that I found 2"o per cent, abnormal out of 319 males 

 captured in the Clyde in 1903. 



Table V. is arranged in such a way that it shows readily 

 not only the variation for the different lots, but also the 

 kind of variation ; and for purposes of comparison Dr 

 Marshall's results are arranged in the same manner along- 

 side. In this Table the letters r. and I. denote the right and 

 left sides, and counting the chelae as the first pair of legs, 

 the walking legs proper are named the second, third, fourth, 

 and fifth pairs from the chelae towards the abdomen. Thus 

 the normal genital apertures are on the fifth and third pairs 

 of walking legs respectively for the male and female Nephrons. 

 The abnormality consists in the occurrence of additional 

 genital openings, for in no case were the normal ones 

 awanting. Nor was any abnormality observed either in 

 the number or in the position of these apertures in the 

 female. Even where openings were shown on both the 

 third and the fifth pairs of walking legs, there was no doubt 

 as to sex, for the modification in the anterior abdominal 

 appendage was always present. In external appearance 

 the extra apertures are very like the normal ones, although 

 occasionally they are slightly smaller, and their relative 

 position on the basal joints of the different walking legs is 

 identical. It will be noted from Table V. that there are no 

 fewer than thirteen distinct variations (B' to N') in the 

 number and in the arrangement of the male genital 

 apertures, and that although bilateral symmetry is so 

 characteristic a feature of Arthropods, those abnormalities 

 occur with very little regard to symmetry. This is further 

 shown in Table VI. The total range of variation, which has 

 come under my observation, is from the normal two apertures 



