216 RALPH DOUG ALL LILLIE 



In such larvae large cells with pale cytoplasm, a large vesicular 

 nucleus with little chromatin, a large nucleolus, and clear kary- 

 oplasm, and but little yolk are found laden with large numbers 

 of dark brown pigment granules. These cells circulate in the 

 blood stream, are seen passing through vascular walls, and are 

 found in the mesenchyme outside. 



In the mesenchyme are also noted a few cells which are some- 

 what less elongated than the rest, more rounded up, and have a 

 more strongly basophil cytoplasm. These probably represent 

 the first lymphoid wander-cells. Toward the end of the phase 

 under description, 3 to 5 mm., the period in which the primitive 

 blood-cells are the only intravascular circulating elements aside 

 from the pigment cells just mentioned, the mesenchyme becomes 

 almost free from yolk, only an isolated cell here and there retain- 

 ing a granule or two. At the end of this phase the primitive 

 blood-cells have lost their spherical form and a portion of their 

 yolk and are now roughly oval elements, all containing yolk, 

 with cytoplasm in varying grades of basophilia, and nuclei con- 

 taining somewhat variable amounts of chromatin, and slightly 

 basophil or very slightly oxyphil karyoplasm. 



My results as to the primitive blood-cells coincide fairly closely 

 with those of Mietens ('10). He states that primitive blood-cells 

 resemble young erythrocytes more than they do primitive leu- 

 cocytes. The primitive blood-cells of Bufo vulgaris are sharply 

 bounded, spherical cells with dark nuclei, rich in yolk. In Lepi- 

 dosiren paradoxa (Bryce, '04) the primitive blood-cells are 

 heavily laden with yolk, show a centrosome with aster, the 

 nucleus is round or oval, not distorted by the pressure of the yolk 

 granules as in Bufo halophilus, sometimes notched, the chromatin 

 is in rounded karyosomes connected by delicate processes to 

 form a reticulum. This, as may readily be seen, corresponds 

 closely to the structure of my primitive blood-cells. Maximow 

 ('10) characterizes the primitive blood-cells of Rana temporaria 

 as large spherical cells, rich in yolk, and those of Acanthias 

 vulgaris are hemoglobin-free, amoeboid, and basophil. In mam- 

 mals (Maximow, '09 a) they are regularly spherical, smoothly 

 contoured cells about 10 to 11.5^ in diameter, in the guinea- 



