SCIENCE- GOSSIP. 



57 



appears also to line the whole scale on its under- 

 side. The explanation seems to be that the scale 

 grows by the addition of a new layer to its under- 

 side, slightly larger than the last, the boundary 

 edge of which forms the characteristic concentric 

 line. In those scales in which the concentric 

 lines do not cross the furrows the outer layers split- 

 as they harden, the interstices being filled with the 

 newly formed transparent matter, and this goes on 

 during the whole of life. The thin flat scale of the 

 eel, which must be searched for beneath the skin, 

 as it does not project from the surface, is a very 

 beautiful object. At first sight, when viewed 

 through a 1-inch objective, it appears to be of a 

 cellular character, but careful study with a J-inch 





^rec.1 WeaCer 



E.U. 

 Fish Scales. 



and a little management of the illumination shows 

 this appearance to be caused by isolated concre- 

 tions of carbonate of lime set in a layer of the 

 same. Similar concretions may be easily seen in 

 several of the scales between the outer laminae and 

 the inner transparent layer. All these scales are 

 very^ beautiful ; some of them are still more in- 



the scales of sole being often exhibited in this way, 

 with the light falling on them in such a manner as 

 to show the comb-like teeth. As transparent 

 objects they can be examined with the spot lens or 

 equivalent arrangement, and with polarised light 

 either with or without a selenite plate. As opaque 

 objects it is only necessary to clean and dry the 

 skin ; as transparent objects the skin must be first 

 dried and then mounted in Canada balsam. The 

 following is the classification suggested by Agassiz, 

 though subsequently modified, as quoted in the 

 " Micrographic Dictionary." Scales enamelled: 

 Ganoid fishes. — -Those the skin of which is regu- 

 larly covered with angular thick scales, composed 

 internally of bone and externally of enamel. Most 

 of the species are fossil, the sturgeon and bony 

 pike being recent. Placoid fishes. — Skin covered 



. Flounder. 



Fish Scales. 



Pla'.ce.. 



irregularly with large or small plates or points of 

 enamel. Includes all the cartilaginous fishes of 

 Cuvier except the sturgeon. As examples may be 

 mentioned the sharks and rays. Many are fossil. 

 Scales not enamelled : Ctenoid fishes. — Scales 

 horny or bony, serrated or spinous at the posterior 

 margin. Contains the perch and many other 



ir, 5 . 



Ba&s 



Pe.rc.lj 



teresting through being mounted as opaque objects. 

 Viewed by polarised light they are of course 

 charming. — J. Lucas. 



I wish a scale of the dog-fish had been added, 

 as a specimen of the " placoid " type. We should 

 then have had three out of the four orders. It is 

 easily obtained on our coast. — Adam Clarke Smith. 



[The foregoing notes, whilst containing nothing 

 original, may be of interest to beginners with the 

 microscope. Fish scales, as stated above, make 

 beautiful objects when viewed with reflected light, 



Sole. 

 Fish Scales. 



existing species, but few fossil. Cycloid fishes. — 

 Scales smooth, horny, or bony, entire at the poste- 

 rior margin ; as the salmon, herring, roach, and 

 most of our edible and freshwater fishes. The 

 majority of the fossil fishes belong to the first two 

 orders, and most of the recent to the third and 

 fourth. The illustrations are from drawings of the 

 original slides made by Miss Florence Phillips, the 

 present Honorary Secretary of the Postal Micro- 

 scopical Society. — Ed. Microscopy, S.-G.] 



Erratum.— Page 26, line 21, column 2, for 

 " grapes " read " grasses." 



