1896.] MICROSCOPICAL JOURNAL 425 



vs. ctenoid scale). Examine a scale from the lateral line, 

 and determine that the line crossing it is a groove which 

 runs obliquely through the scale from the front inner side 

 to the hind outer side (this in life lodges the ending of a 

 nervous organ). Illustrate these points. 



Examine the general skin with a hand lens and note 

 that the black color is caused by minute black spots, which 

 are closely set, but ventrally are located in rows crossing 

 so as to form diamond-shaped areas; how do these areas 

 compare with the location of the scales? Cut off care- 

 fully taking as little as possible of the sub-jacent tissue 

 a portion of the skin surrounding one of these areas, 

 mount it in water and examine (low-power) now you will 

 see that the spots are peculiar objects with irregular 

 radiating processes, they are "pigment cells" and their 

 growth is the cause of the color of the skin. They are a 

 variety of "connective tissue cell" which has taken on the 

 function of pigment secretion. 



Examine the same piece (high power) you will find 

 that it is composed of ^^arallel fibres, ''dermis," in two 

 sets crossing each other, they are "white fibrous tissue" 

 a second variety of connective tissue; white fib. tiss. 

 swells and become translucent when treated with acetic 

 acid, irrigate the piece and note the reaction, the fibres 

 becoming invisible after its action. Draw views to show 

 the location of the pigment cells, their shape, and the 

 crossing fibres of the "dermis." 



{To he continued!) 



The Plague of Mice in Russia. 



The Consular Reports for April contain a long con- 

 tribution on the above subject, collated from a number 

 of Russian governmental sources. Southern Russia and 

 Siberia have during the last three years been the scene 

 of the rise and fall of a pest of mice. In some places 



