BLOOD AND BONE-MARROW OF FROG 443 
and 19). The latter may be simple, bilobed, or double (diplo- 
some). These cells were never seen in mitosis in the circulating 
blood. The persistence of such a definite and conspicuous at- 
traction sphere in a cell whose nucleus undergoes successive 
constrictions in the formation of a polylobular condition (figs. 13 
to 21) is of much theoretical interest, a point which will be dis- 
cussed below in connection with its myelocytic history. 
The relationship between the two types of attraction spheres 
is not perfectly clear. However, they correspond closely with 
similar types occurring in other cells, e.g., maturing eggs of 
Cummingia,? where the clear sphere with its central granule 
-(centrosome) of earlier stages becomes converted into a granular 
darker sphere through division of the centrosome. In these 
leucocytes of the frog the monosome and diplosome occur more 
commonly in those cells with the less complex nucleus, the finely 
granular spheres in those with the more complex polymorphous 
nucleus (compare fig’. 13 and 19 with fig. 25). Though figures 
16 and 24 show that this relationship is not invariable, it may be 
said that no cells with nuclei like that of figure 13 were seen with 
the granular type of sphere. The inference seems justified that 
here also the granular type of sphere arises from the clear type 
with diplosome, by repeated division of the centrosome. The 
granular type would thus represent a disintegration or partition 
product. The bearing of this conclusion will be discussed in 
connection with the description of these same features of the 
medullary neutrophilic leucocytes, where also these same two 
types of attraction spheres occur. 
6. The thrombocytes. These cells typically are stout fusiform 
elements with central, deeply staining (violet), dense, oval 
nucleus (figs. 28 and 30). The cytoplasm stains only very faintly 
(pink) and contains metachromatic spherical granules of uni- 
form size. These granules appear identical with the larger 
granules of the neutrophilic leucocytes. The granules are gen- 
erally aggregated more or less closely into small groups. The 
cytoplasm is apparently extremely viscid and is drawn out at 
numerous points into pseudopod-like projections (figs. 27 and 
31). These contain the majority of the granules. Certain of 
