CHAPTER XL 



linear series — continued. 



Miscellaneous Examples. 



In this chapter are given some miscellaneous examples. Most 

 of them illustrate the Meristic Variation of parts standing in 

 bilateral symmetry on either side of a median line. 



Here also are included certain cases of Variation concerning 

 the series of apertures in the shell of Haliotis, though probably 

 they are of a wholly different nature. 



Scales. 



Among animals possessing an exoskeleton composed of scales, 

 the number of the scales or of the rows of scales found in par- 

 ticular regions is usually more or less definite. So constant are 

 these numbers in their range of Variation that in both Reptiles 

 and Fishes either actual numbers or certain ranges of numbers are 

 made use of for purposes of classification. 



Considerable Variation in these numbers is nevertheless well 

 known, and many instances are given in works dealing with 

 Reptiles or Fishes. The following cases are given as illustrations 

 of some of the larger changes which may occur. 

 403*. Clupea pilchardus (the common Pilchard). Among the 

 Pilchards brought to the curing factories at Mevagissey, Corn- 

 wall, specimens have from time to time been found by Mr Mathias 

 Dunn, the director, having the scales of one side very many more 

 in number than those of the other side. Two specimens 1 shewing 

 this abnormality were given to me by Mr Dunn in 1889. Owing 

 to the fact that the fresh Pilchards are shovelled wholesale into 

 the brine-vats, it is not until the fish are picked over for packing- 

 after the salting process that any individual peculiarities are 



1 These specimens are now in the Museum of the Royal College of Surgeons. 

 An account of them was published in P. Z. S., 1890, p. 586. Figures of the same 

 variation were given by Day, F., P. Z. S., 1887, p. 129, PI. xv. 



