DEPARTMENT OF EMBRYOLOGY. 107 



have considered this process as a normal way for cell multiplication. 

 Dr. Macklin has devoted his attention to the fate of cells with elongated 

 or constricted nuclei, and of mononucleated and multinucleated cells 

 as observed in living cultures of embryonic chick tissue. He found 

 that the constriction of the nucleus may end in amitosis and that 

 repetition of the process may produce multinucleated cells. In no 

 case has it been found that the parts became separated to form the 

 nuclei of mononucleated cells. The only change which took place in 

 these cells (some of them being observed for 12 hours continuously) 

 occurred when they were undergoing mitosis. There was a disappear- 

 ance of the nuclear membrane with a fusion of the karyoplasm of the 

 two nuclear moieties and the formation of a single amphiaster. In this 

 way there finally resulted two apparently normal nuclei contained 

 within separate cells. These observations contradict the opinion 

 gained through observation of fixed material, according to which cells 

 may multiply by amitosis, and indicate that amitosis is a change in 

 form of the nucleus rather than a method of cell proliferation. 



Another contribution to the behavior of embryonic chick tissue in 

 cultures has been made by Dr. Paul G. Shipley. A first group of 

 cultures was made with tissue taken from the area opaca, before the 

 formation of blood-islands and the elaboration of hemoglobin, and 

 grown in the blood-plasma of an adult hen. In many cultures young 

 erythrocytes were found which developed from undifferentiated, 

 highly amoeboid, very small, mononuclear elements. The process of 

 erythrogenesis was initiated by a cessation of amoeboid movement. 

 The cell withdrew its processes and became round. The round hemo- 

 globin-free cells still had the power of multiplication by mitosis, but 

 usually hemoglobin was elaborated without further division, with the 

 resulting formation of the hemoglobin-bearing erythrocytes. In this 

 way a small number of nonnal red cells were produced in cultures, but 

 most of the erythrocytes differed in many respects from the normal 

 type, which under the condition existing in the cultures should not be 

 surprising. Several cultures showed, after 24 to 30 hours, the develop- 

 ment of the heart-muscle, which began to beat rhythmically. Regu- 

 larity in beat was not maintained for over 24 hours ; after this time the 

 rate became slower and slower until it ceased ; pulsation could, however, 

 for a time be reinduced by mechanical or thermal stimulation. These 

 facts show that the Ufe of cells in cultures in not merely a series of 

 "survival phenomena" on a down-grade of progressive differentiation. 



Professor Eliot R. Clark studied the reaction of mesenchyme cells 

 in the tadpole's tail toward injected oil-globules. His investigation 

 was undertaken in order to find out the reaction of the mesench3mie 

 cells to the pressure of globules of fluid artificially introduced into the 

 tissue-spaces. The problem is interesting in its relations with the 

 formation of lymphatic vessels. One view is that the lymphatics are 



