150 Proceedings of the Royal Physical Society. 



individuals now under consideration, and because, like Dr Marshall's example 

 with seven apertures, it had an opening on one of the second pair of legs. 

 This specimen had a single aperture on the second right leg, oue on the third 

 left leg, and one on each of the right and left legs of the fourth and fifth pairs 

 of legs. The example with a single aperture on the fifth right leg (already 

 referred to), and the other example with an opening on each leg of the third 

 and fifth pairs of legs (also already referred to), show two arrangements of 

 genital openings which, so far as I can ascertain, have not been previously 

 recorded. It is worthy of remark that in every case where supernumerary 

 spermatic openings occurred, the normal openings were also 

 present. 



In the present instance, 213 abnormal males have been noted out of 1988 

 males examined. This shows an abnormality of 107 per cent, in the number 

 of spermatic openings. It will be observed that these examples exhibited 

 thirteen different arrangements of the genital apertures. Including the 

 arrangement of seven apertures which Dr Marshall gives, the arrangement of 

 six apertures which I have previously recorded, and the normal type, we 

 have thus a record of sixteen different arrangements of these openings in 

 Nephrops norvegicus. The total range of variation, which has come under my 

 observation, is from 1 to 6 genital openings. 



Of the forms showing variation 



0'5 per cent, had 1 genital opening. 



72-3 „ 



„ 3 genital openings. 



211 



4 



47 „ 





1-4 „ 



1J ^ >) M 



This series shows how great is the tendency towards an increase in the 

 number of genital apertures, and also how markedly the number of abnormal 

 forms decreases as the extent of the abnormality increases. 



From the following comparative Table it is seen that 4491 of the Norway 

 lobsters sent to Edinburgh University Zoological Laboratory have been 

 examined with the view of ascertaining the extent of variation in the number 

 and arrangement of genital openings. Lot A consists of those examples 

 which Dr Marshall {op. cit.) examined in 1901 ; Lot B, those which I 

 examined {op. cit.) in 1906 and 1907; and Lot C (the present collection), 

 those which I examined between the summers of 1907 and 1910. We have 

 thus a record of all the specimens sent to the Laboratory during the past 

 six years, all obtained (as well as Dr Marshall's lot) under exactly the same 



