GH. VIII] FROGS, TOADS, AND NEWTS 257 



ovaries as the sex may be. They develop from the 

 anterior portion of the genital ridges whose posterior 

 portions alone give rise to the sexual organs 1 . In the 

 autumn they are of great size and loaded with fat-cells, 

 a certain amount of lymphatic tissue being also present. 

 In the spring they are much reduced. It is probable that 

 they also perform other functions at all seasons of the year, 

 but on this point we have no precise knowledge. 



Circulation. The blood consists of a clear, almost 

 colourless fluid, the plasma, in which float corpuscles of two 

 sorts ' red ' and colourless. The former are by far the 

 more numerous, though the exact proportion is subject to 

 considerable fluctuation. The 'red' corpuscles are oval 

 discs, about O02 mm. long by 0*01 mm. wide, containing 

 an oval nucleus which causes the central region of the disc 

 to bulge outwards on each face. Their colour is yellow 

 rather than red, though when any thickness of them is 

 seen they produce a red effect. The colouring matter is 

 haemoglobin; it acts as a carrier of oxygen from the 

 respiratory organs to the general tissues of the body. The 

 colourless corpuscles are of several different varieties and 

 sizes, but are smaller than the 'red'; they possess the 

 power of independent movement like an Amoeba and 

 contain one or more nuclei. They can also migrate 

 through the walls of the blood vessels and are found in 

 nearly all tissues of the body, but especially in. the 

 connective tissues. They probably play an important part 

 in the removal and repair of effete or injured tissues, and 



1 Marshall and Bles, Studies Biol. Lab. Owens Coll. n. ; cf. Giles, 

 Q. J. If. S. xxix. 



L. 17 



