438 H. E. JORDAN 
Since the latter cell, under certain conditions, becomes the source 
of the blood-platelets, interest centers also on the amphibian 
homologue of the mammalian platelet. 
It became apparent early in this investigation that a confi- 
dent interpretation of the developmental stages of the hemal 
elements of the marrow demanded a precise knowledge of the 
types of cells of the circulating blood. Accordingly, blood and 
marrow were: studied coincidentally and with the same tech- 
nics. As regards the blood, the cells of special importance in 
this connection are the polymorphonuclear neutrophilic leuco- 
cytes and the spindle cells, both containing similar metachro- 
matic (azurophil) cytoplasmic granules. 
In the red marrow the origin and development of these same 
elements claim first attention. Incidentally must be con- 
sidered also the developmental history of the eosinophilic and 
basophilic leucocytes, the origin of the lymphocytes and of the 
erythrocytes, the genetic relationships among the several series 
of blood-cells and the bearing of these data on the prevalent 
monophyletic theory of blood-cell origin. 
MATERIAL AND METHODS 
The species of frog used in this work is Rana pipiens. Smear 
preparations of blood were stained according to Wright’s technic. 
The frogs employed had been left over from the early fall, kept 
in cages until the middle of January. Blood smears were made 
in October, in January, and in April. The bone-marrow was 
taken from the femurs of frogs killed in January, in a certain 
number of which the shaft was well filled with red marrow. 
The marrow was fixed in a mixture of 100 parts of a saturated 
normal-salt solution of corrosive sublimate and 10 parts of forma- 
lin. Paraffin sections were cut at 54 and stained according to 
Wright’s® technic. This technic gave very excellent results. 
