Genital Apertures in the Norway Lobster. 145 



XVII. — Observations on the Number of Genital Apertures and on 



the Disproportion of Sexes in the Norway Lobster (Nephrops 



norvegicus). By D. C. M'Intosh, M.A., B.Sc, F.R.S.E. (From the 

 Zoological Department of Edinburgh University.) 



(Read 24th October 1910. Received 25th October 1910.) 



During each session there are brought to the Zoological Department of 

 Edinburgh University, for use in the Laboratory, several boxes of Norway 

 lobsters. For some years it has been my privilege to examine each boxful 

 as delivered. All are procured from the fish-market at Newhaven, whither 

 they are brought by Granton trawlers. It is well known that there occur 

 individuals with additional spermatic apertures, and the main purpose of my 

 examination has been to ascertain the percentage showing this abnormality. 

 Incidentally some other observations were made, and in particular the 

 proportion of the sexes was noted. 



"While Bateson 1 in his " Materials " makes no mention of variation in the 

 number of genital apertures of Nephrops norvegicus, he gives interesting 

 records relating to Astacus fluviatilis. Marshall, 2 in a communication in 

 1902, says : " The only published record, so far as I know, of additional 

 genital openings in Nephrons, is a recent paper by Mr Cole, who states that 

 ' abnormalities in oviducal and spermatic apertures are by no means 

 uncommon.' " Marshall's communication deals with his record of observations 

 made on 1068 Norway lobsters, in the Zoological Laboratory of Edinburgh 

 University, in 1901. In the autumn of 1906, I examined 630 specimens 

 preserved for dissection purposes in the Zoological Laboratory. Durino- 

 session 1906-7, three additional boxfuls, each containing on the average 243 

 specimens, were also examined. An account of my observations on these 

 1359 examples, as well as on 3689 procured for other purposes, but also 

 captured in the North Sea, has been published. 3 In the interval, between 

 the summers of 1907 and 1910, there have been brought to Edinburgh 

 University Zoological Laboratory 2064 Norway lobsters, and it is now 

 proposed to consider the further record of abnormalities observed during 

 these consecutive years. 



1 Bateson, W., Materials for the Study of Variation. London, 1894. 



2 Marshall, F. H. A., " On Variation in the Number and Arrangement of the Male 

 Genital Apertures in the Norway Lobster," P.Z.S., pp. 2-12. London, 1902. 



3 M'Intosh, D. C., " Variation in the Norway Lobster," Proceedings of the Royal Physical 

 Society of Edinburgh, vol. xvii. pp. 129-142. 1908. 



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