76 HOWELL. [Vol. IV. 



{2'S), in his Cartwright lectures, describes in the adult marrow 

 seven different kinds of cells. He derives the nucleated red 

 corpuscles, in the first place, from a colorless cell 9 to 12 /x. 

 in diameter, with a smooth, homogeneous protoplasm and a 

 finely granular nucleus. This cell shows, moreover, a pecu- 

 liar flexibility. These cells, in turn, are derived from what he 

 calls "protoleucocytes," which are solid-looking lymj^hoid ele- 

 ments, 2.5 to 5 /A. in diameter, resembling free nuclei, though 

 some of them may have a narrow rim of protoplasm. The 

 nucleated red corpuscle is transformed to the non-nucleated 

 corpuscle by the gradual disappearance (absorption) of the 

 nucleus, after which the corpuscle becomes condensed to the 

 flattened disc shape. 



The most elaborate, and probably the most important, con- 

 tribution to our knowledge of the development of the red and 

 the white corpuscles which has been made recently is found 

 in a series of papers by Lowit (29). The most important con- 

 clusions at which he arrives are as follows : the blood-forming 

 organs of the adult, among the cold-blooded as well as the 

 warm-blooded animals, are the bone marrow, the spleen, and 

 the lymph glands. In all of these organs we meet with two 

 kinds of colorless cells. One of these he calls " leucoblasts " ; 

 and they are destined to form the leucocytes of the blood and 

 lymph. To the second he gives the name of " erythroblasts" : 

 from these the red corpuscles are developed. These two sorts 

 of cells are distinguished from each other by differences in the 

 structure of the nucleus, in the method of multiplication, and 

 in the properties of the cell protoplasm. The leucoblasts have 

 a nucleus which is relatively quite large. It contains one or 

 more small heaps of chromatin, sometimes irregular in shape, 

 from which a system of delicate lines and bands radiates toward 

 the nuclear membrane. This latter consists of a distinct, often 

 doubly contoured, band of chromatin substance, on the inner 

 side of which one frequently finds irregular projections con- 

 nected with the intra-nuclear network. The leucoblasts mul- 

 tiply by a process less complicated than ordinary karyokinesis 

 and more complicated than simple direct division. The chro- 

 matin granules during division show some movement, though 

 of an irregular character, from the equator toward the poles. 

 He proposes to call this divisio per gramda. The erythro- 



