458 SUMMAEY OF CUJ{RENT RESKARCHES RELATING TO 



account for the absence of the gall-bladder in these three cases. In the 

 rat it is possible that the rapid and early reduction in size of the yolk- 

 stalk, which leaves the forearut wall quite short antero-posteriorly, may 

 be a factor in inhibiting the development of the gall-bladder. In 

 Mammals generally, as compared with most lower forms, there is a 

 distinct shortening of the liver primordium and a tendency towards 

 consolidation of the cystic and hepatic portions. This has been well 

 shown in Pensa's recent work on Bos taurus, and it may be that the 

 rat is but an extreme example of the consolidation. 



It is possible that there are in man two types of casual inhibition of 

 the development of the biliary apparatus. In one type the entire pars 

 cystica of the liver primordium is suppressed, and this would be repre- 

 sented by the rare cases in which both gall-bladder and bile-ducts are 

 absent. In the other type only the gall-bladder primordium is lost, 

 either early or late in development, and this would be represented by 

 the more common anomaly of the absence of the bladder only. The 

 large size of the bile-ducts is noticeable in both pigeon and rat embryos. 

 This seems to be a compensation for the absence of the usual bile 

 reservoir in the form of a definite sac. 



b. Histolog-y. 



Functional Significance of Mitochondria.* — E. V. Cowdry defines 

 mitochondria provisionally as substances which occur in the form of 

 granules, rods and filaments in almost all living cells, which react 

 positively to janus green, and which by their solubilities and staining 

 reactions resemble phospholipins (complex compounds of fatty acid, 

 phosphorus and nitrogen), and to a lesser extent, albumins. Chemically 

 they may be combinations, in varying amounts, of phospholipins and 

 protein. They play an active part and fundamental role in cell activity, 

 though just what the part is remains obscure. In early stages of 

 development they are the only formed elements in the cytoplasm. The 

 movements of mitochondria in living cells tend to confirm mistrust in 

 the doctrine of a cytoplasmic reticulum. 



Wandering Cells in Loose Connective Tissue of Bird.f — Vera 

 Danchakoff has studied the many kinds of amoeboid cells found in the 

 loose connective tissue of the hen. Some of them are the direct 

 descendants of the amoeboid cells produced by the mesenchyme of the 

 embryo. The embryonic mesenchyme appears to be a diffuse primordium 

 for both lymphopoiesis and granuloleukopoiesis, and there remains a 

 power of similar differentiation in the whole loose mesenchyme as well 

 as in special haematopoietic organs. The mesenchyme is polyvalent in 

 its potencies of development, the differentiation in various directions 

 (different kinds o'f blood-cells), being directed by the environing 

 physiological conditions. 



* Amer. Journ. Anat., xix. (1916) pp. 423-46. 

 t Anat. Record, x. (1916) pp. 483-92. 



