Genital Apertures in the Norway Lobster. 151 



conditions (so far as these are known), and all examined without 

 selection. 



Comparative Table. . 



Lots. 



Number of 

 Individuals. 



Total Males. 



Normal 

 Males. 



• !' 



Percentage 

 Abnormal ', of 

 Males. Abnormal 

 Males. 



Total 

 Females. 



A 

 B 

 C 



1068 

 1359 

 2064 



1000 

 1249 

 1988 



878 

 1167 

 1775 



122 



82 



213 



12-2 

 63 



10-7 



68 



110 



76 



Totals 



4491 



4237 



3820 



417 



9-8 



254' 



A study of this Table shows how accurately Dr Marshall summed up 

 the facts when he remarked (pp. cit, p. 8) : " That Norway lobsters with 

 additional genital apertures have been common in Scottish waters for a 

 considerable number of years, appears from information supplied me by 

 Professor Ewart, Dr Beard, Dr Masterman and others. Before I began my 

 investigation on the degree of frequency of such abnormal lobsters, Dr 

 Masterman expressed the opinion that quite 10 per cent, of the specimens he 

 had observed since he had been in Scotland had additional genital openings." 

 From the Table given, it is seen that 9 - 8 per cent, of the 4237 male specimens 

 had other than the normal two spermatic openings. As indicating the fallacy 

 resulting from examining occasional boxfuls, the following are some of the 

 percentages of abnormal males found — 10 - 5 per cent, of 238 specimens, 14 - 5 

 per cent, of 268 specimens, and 4"! per cent, of 169 specimens. 



DISPPOPOKTION OF SEXES. 



A remarkable feature of the Table given is the small percentage of females. 

 In Lot A Dr Marshall found 64 per cent., and in seeking for an explanation 

 of the relative scarcity of females, he suggested that probably " the majority 

 of them had migrated to a greater distance from laud " (op. cit., p. 6). In Lot 

 B there were 84 per cent, females, and in commenting on this (op. cit., pp. 

 136-138) I sought for an explanation in the fact that females, being distinctly 

 smaller than males, may escape through the meshes of a trawl net in greater 

 numbers. I gave statistics of actual measurements showing the relative size 

 of the sexes, and I also showed how much greater is the proportion of females 



