THE FLOUNDER AND THE PLAICE. 295 



the term. An examination of the tables given for plaice reveals the fact 

 that the majority of tlie specimens examined varied in length from 20-30 

 cms, (about 8-12 in.). To assume that all these individuals were "grown 

 up," and that the influence of age need not therefore be considered, is to 

 assume what appears to us to require proof. Our author himself points 

 out that the influence of age might be such as to lead an observer to 

 erroneous conclusions with regard to the influence of locality. But he 

 neither investigates the relation of differences in age to any particular 

 character, nor does he examine for each locality a sullicient number of 

 individuals of about the same size to render it probable that the 

 differences due to variation in age may be safely left out of considera- 

 tion. It is clear that if a sufficiently large number of forms of the 

 same size were examined, the characters for flshes from each locality 

 might be considered in relation to the most probable age for that size. 

 But even so, the influence of the locality on the rate of growth would 

 have to be determined. 



With regard to the influence of sex, our author states that in both 

 species the females are always broader, and have longer heads than the 

 males. In the males the number of vertebrae is somewhat smaller than 

 in the females. 



The subject of the development of scales in the two species is next 

 considered. To this we would draw special attention, as it is in respect 

 of the character of the scales that the two species differ most strikingly 

 from one another, and the author's observations on the point are 

 distinctly interesting. It is pointed out, that in both species cycloid 

 scales begin to develop (when the fisli is 1-5-20 cms. long) over the 

 whole surface of the body, at the bases of the caudal fin rays, on the 

 cheeks and on the prreoperculum. The plaice develops these scales on 

 the ocular side along the inside rays of the dorsal and anal fins, and at 

 the bases of the pectoral and ventral fins. The scales lie embedded in 

 the skin, separated for the most part from one another, and it is only in 

 particular parts, for instance the caudal peduncle on the ocular side, that 

 they overlap. In the female plaice, development of scales rarely 

 proceeds beyond this stage ; in the male, changes may occur after 

 maturity has been reached, but these changes only consist in a transfor- 

 mation of the cycloid scales into the ctenoid condition. In the flounder, 

 on the other hand, the cycloid scales become transformed in various 

 parts of the body into a ctenoid, and even more complicated condition, 

 while the fish is still only 2-3 cms. long. 



The change of a cycloid into a ctenoid scale proceeds in the following 

 manner : — The posterior edge of the scale becomes raised out of the 

 enclosing epithelium, and a layer of hard transparent substance bearing 

 spines is laid down over the surface of the scale. This layer, which is 



