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Part III. — Eighteenth Annual Report 



Sea the female does not reach maturity, on an average, until 

 attaining a length of about 15^ inches, and the male on the average 

 at a length of twelve to thirteen inches. The variability of the 

 sexes, and variations due to growth are considered in detail ; and 

 with regard to the question of race-variability, it is shown that the 

 North Sea plaice are divided into at least two groups by definite 

 and distinct differences in structure. The plaice of the southerly 

 North Sea are relatively more elongated and narrower, while those 

 of the northern parts of the North Sea are relatively broader and 

 shorter. The causes of their difference and variability are discussed, 

 and the paper is illustrated by a number of tables and diagrams. 



The Classification of Flat-Fishes. 



A paper on this subject is also furnished by Mr. Kyle, in which 

 the affinities and classification of the various species and genera of 

 flat-fishes are considered in great detail. The species examined 

 included the majority of the European forms, representatives of the 

 chief genera of the American flat-fishes, and of the Indian, China, 

 and Australasian seas. Their structure and distribution are 

 described, and their natural affinities, as far as possible, deter- 

 mined. The paper, which is illustrated by two plates, embodies 

 the results of a large amount of work, and forms a valuable addition 

 to our knowledge of the subject with which it deals. 



The Invertebrate Fauna. 



Another paper is furnished by Mr. Thomas Scott, in which he 

 gives additional observations on the crustacean fauna, and describes 

 a number of species belonging to the various groups, which were 

 for the most part obtained by the Garland in the seaward part of 

 the Firth of Clyde and in Loch Fyne. Some of the Copepoda are 

 new to science, and with regard to those previously recorded, 

 further information has been obtained regarding their structure and 

 distribution. The paper is illustrated by two plates. 



ANGUS SUTHERLAND, Chairman. 



D. CRAWFORD, Deputy-Chairman. 



D'ARCY W. THOMPSON. 



J. RITCHIE WELCH. 



W. R. DUGUID. 



L. MILLOY. 



D. MEARNS. 



WM. C. ROBERTSON, Secretary. 



