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WILBUR WILLIS SWINGLE 
mesodermal cells from the mesentery and mesonephros (the so- 
called sex cords, a misnomer for they are in reality the anlagen 
of the- rete or efferent apparatus) . 
Various fixatives have been employed, such as Flemming, Bou- 
in's, Ezra Allen's ('16) modification of Bouin's fluid, and others. 
The best results were obtained with the last two fluids. The 
mesonephros was usually left attached to the testis. Sections 
were cut at a thickness of 8 to 10 m- Even at this thickness it 
Fig. 1 a) Gonads of animal of first year. Average total length of larvae, 40 
to 50 mm.; b) gonads of tadpoles 70 to 95 mm. total length; c) gonads of tadpoles 
nearing metamorphosis; total length, 120 to 150 mm. 
is necessary to reconstruct the nucleus in most cases because of 
the large size of the cells. All spermatogonial counts, however, 
were made from complete cells. 
The larvae used for the present work were taken from various 
localities and during different seasons of the year. Four hundred 
larvae rneasuring from 70 to 110 mm. were taken from the ponds 
of the State Fish Hatchery, Pratt, Kansas, during the month of 
September, 1917; 300 larvae averaging 100 mm, were taken from 
pools in the vicinity of Lawrence, Kansas, in the fall of 1916; a 
group of 1500 larvae averaging 70 mm. was caught in August, 
