ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 367 



granules. There is some indication in the arrangement of the planes of 

 a division of the early myocardium into mononuclear cell areas which 

 correspond to lobations on its exterior. J. A. T. 



Giant-cells of Yolk-sac and Bone-marrow.— H. E. Jordan (Amer. 

 Jour/i. Anat., 1918, 24, ■22b-6[), 70 hgs.). The giant-cells of the 

 marrow of young bones are of two physiological types, htemogenic and 

 osteolytic. They agree in being multinucleated and in possessing 

 originally a basophilic cytoplasm, which gradually becomes oxyphilic. 



The hemogenic giant-cells or polykaryocytes originate from hyper- 

 trophied hemoblasts by dirrct division of the nucleus of transitional 

 polymorphokaryocytes. They are essentially multiple ha3moblasts and 

 may differentiate erythrocytes intracellularly under certnin conditions, 

 apparently such as call for increased hfemopoietio activity. They are 

 the same in yolk-sac and red bone-marrow. 



There is no unequivocal evidence that polymorphokaryocytes and 

 haemogenic polykaryocytes are phagocytic. They may perhaps I'epresent 

 an incidental phase of intense hemopoiesis. 



The osteolytic giant cells (osteoclasts of Kolliker) originate from the 

 marrow reticulum by a process involving the aggregation of nuclei 

 within larger cytoplasmic masses and secondary fusion with other 

 portions of the reticulum and with osteoblasts. They may during their 

 early stages of differentiation produce blood granulocytes, or possibly 

 hsemoblasts, but there is no direct genetic homology between them and 

 polykaryocytes. They eventually disintegrate and are not re-transformed 

 into marrow reticulum. J. A. T. 



Histology of Lymph. — H. E. Jordan {Anat. Record, 1918, 16, 

 37-45). The primary object of this investigation was to determine 

 whether blood-platelets occur in lymph. The material employed con- 

 sisted of smear preparations of lymph from the thoracic duct of the dog. 

 The evidence seems conclusive that platelets are preformed structural 

 elements of blood — not precipitated products — and that they do not 

 form a normal constituent of the lymph of the thoracic duct. Tbis may 

 mean that only a small quota is contributed to the peripheral portion of 

 the lymphatic tree, and that disintegration occurs during their relatively 

 slow progress towards the thoracic duct. J. A. T. 



Iridocytes in Batrachian Larvae. — C. R. N. Rao (Records Indian 

 Musejim, 1917, 13, 281-92, 1 pi.). The larvae of Microhyla ornata 

 and M. rubra float on the surface in shoals. This habit is correlated 

 with the presence of air-chambers between the branchial plates, which 

 function more or less as hydrostatic organs. The attacks of enemies 

 are warded off by the presence of an acid offensive matter in the 

 cephalic gland, and this is probably advertised by the bright coloration. 

 There is a unique occurrence of iridocytes (with guanin crystals) and 

 argenteum or reflecting tissue. The presence of iridocytes and black 

 (melanin) chromatophores on the lungs and peritoneum is very interest- 

 ing, for both these occur in the air-bladder and peritoneum of some 

 embryo fishes. The iridocytes of the mid-dorsal band and the ventral 

 argenteum of the sub-cutaneous tissue of the abdomen are free from 



