1902,] VARIATION IN THE NORWAY LOBSTER. 11 



agreeing " in all their relations with those of Pervpatus" and the 

 probability of their being derived from nephridia he regards as 

 " very great." It is, however, very doubtful whether the case of 

 Nephrops has any real bearing on this question, seeing that in 

 Astacus we may also get variation in the dii-ection of reduction of 

 apertures, and in Camharus simple homceotic shifting of the 

 apertures without any addition to their number. 



However this may be, the occurrence of such a high percentage 

 of a particular kind of abnormality as I have recorded among the 

 Norway lobsters of the Forth area during the present year is 

 instructive as supplying another example of the falsity of the 

 doctrine that a well-marked variation cannot exist with any con- 

 siderable degree of frequency owing to the so-caUed " swamping 

 eifects of intercrossing." 



Specimens illustrating the various arrangements of the genital 

 apertvires described in this paper were exhibited before the 

 Zoological Section of the Meeting of the British Association at 

 Glasgow. 



In conclusion I must express my indebtedness to Mr. Bateson, 

 by whom I was induced to undertake this investigation. 



References to Literature. 



Allen. — "Nephridia and Body-cavity of some Decapod Criastacea." 



Q. J. M. S. vol. xxxiv. p. 403 (1893). 

 Bateson. — " Materials for the Study of Variation." London, 



1894. 

 Benham. — " Note on a Couple of Abnormalities." Ann. & Mag. 



Nat. Hist. vol. vii. p. 256 (1891). 

 Bergendal. — " TJeber abnorme Formen der ersten abdominal en 



Anhange bei einigen Krebsweibchen," Bihang till K. Sv. 



Vetenskaps-Akad. Handlingar, vol. xiv. Stockholm, 1889; 



and " Neue Beobachtungen iiber die Form variation der 



ersten abdominalen Anhange bei Krebsweibchen," ibid. 



vol. XV. 1890. 

 Ogle. — " Some Yariations in the Spinal Nerves of the Frog." 



Trans. Liverpool Biol. Soc. vol. xv. p. 114 (1901). 

 Desmarest.— " Note sur une Disposition anormale des Organes 



genitaux observee dans VAstaciijS Jiuviatilis Fabiicius." 



Annales de la Societe Entomologique de France, 2^ serie, 



vol. vi. p. 479 (1848). 

 Faxon. — " On some Crustacean Deformities." Bull. Mus. Comp. 



Zool. vol. viii. p. 257 (1881). 

 Faxon. — " Revision of the Astacidse." Mem. Mus. Comp. Zool. 



Camb., Mass. vol. x. 1885. 

 Faxon. — " Observations on the Astacidas in U.S. National Mus. 



and in Mus. Comp. Zool.," &c. Proc. U.S. Nat, Mus. vol. xx. 



p. 643 (1898). 

 Huxley.—" On the Classification and the Distribution of the 



Crayfishes." P. Z. S. 1878, p. 752. 



