THE FLOUNDER AND THE PLAICE. 297 



we spoke above is not to be got at by striking an average for each of 

 the separate characters examined in the individuals from the region in 

 question, but rather by determining not merely the amount of any 

 abnormality, but also the degree to which it is associated with other 

 abnormalities. We think we are right in saying that tlie laws of 

 correlation do limit, and to some extent determine, the directions which 

 evolution may take. In dealing with local forms, these considerations 

 ought not to be ignored. 



We may make our point of view clearer by reference to the formulae given 

 by our author, which denote what he calls the " extreme flounder form," 

 or the " extreme plaice form." These formula are arrived at by taking 

 the extreme variations of the several characters in the flounder and the 

 plaice, contrasting them in this way as much as possible. The formulae 

 thus obtained represent the sum of a number of separate possibilities ; 

 but it by no means follows that the several extreme characters, which 

 are separately possible, are possible in combination with one another in 

 a single individual, and, in point of fact, as an examination of the 

 tables shows, there is not a single instance of either of these extreme 

 forms among the individuals examined by the author. 



Our author having, as the result of his investigation into the local 

 forms, taken up the position that the relationship between the two 

 species in the Baltic is closer than in the North Sea, finds support for 

 this view in the existence of an intermediate form which inhabits the 

 south-western part of the Baltic, and which was first described by 

 Gottsche as a variety of the plaice, and named Plcuronectes pseudojlesus. 

 This form differs from the flounder in having cycloid scales on its 

 " blind side," and the ctenoid scales of the plaice on its ocular side. 

 It differs, however, from the latter species, and approaches the former in 

 having rows of scales on its lateral line, and on the bases of the dorsal 

 and anal fin rays, which are more highly developed than the ctenoid 

 scales, and represent, in fact, a stage in the development of the scales 

 which is characteristic of the flounder. The question arises, whether it 

 is an intermediate form or a hybrid. On the one hand, the fertility 

 of the fishes would seem to point to the former hypothesis ; on the 

 other, the mingling of the specific characters (of the flounder and 

 the plaice), and the rarity of its appearance, would seem to support 

 the latter. Our author inclines to support the latter view, in opposition 

 to Mobius and Heincke, "ohne dass ich einen wissenschaftlichen 

 grund hierfiir anzugeben vermcichte." 



A form has been described by Ekstrom and Smitt which is also 

 intermediate between the flounder and the plaice, and differs very 

 slightly from Fleuronectcs psendojlesus. This form, to which the name 

 /'/. ijlaciaiis has been given, is found on tlie western part of the 



