DEVELOPMENT OF WANDERING MESENCHYMAL CELLS 109 



go, and further give an opportunity to test the influence of the 

 circulation on the mode of differentiation and function of the 

 mesenchymal cells. 



The prevention of the circulation has been accomplished in 

 the same manner as employed in the previous investigation and 

 fully described in the September number of this journal. The 

 eggs shortly after being fertilized are placed in solutions of alcohol 

 in sea-water. The series of solutions most advantageously used 

 is prepared as follows: 1.5 cc., 2 cc., 2.2 cc., 2.4 cc., 2.6.cc., 2.8 cc., 

 and 3 cc. of 95 per cent alcohol is added to 50 cc. of sea-water. 

 These solutions are renewed after twenty-four hours and after 

 another twenty-four hours the eggs are placed in pure sea-water. 



Such a series gives, of course, gradiations of the effect. Eggs 

 in the weaker solutions develop normally in many cases, while 

 other individuals develop slightly slower than the normal and 

 have the circulation of their blood arrested to different extents. 

 Many individuals in all of the solutions fail entirely to establish 

 a blood circulation and although the heart pulsates feebly it 

 does not propel the plasma for one or another reason which 

 has been previously discussed. In spite of the failure of the 

 blood to circulate, the development of the cells on the yolk-sac 

 progresses in an almost normal fashion and vessels and blood 

 corpuscles arise in this region and may be carefully observed 

 throughout the life of the embryo. 



The observations on the living yolk-sac have been supple- 

 mented by a study of fixed and cleared specimens. Embryos 

 at different stages of development are fixed in a saturated solu- 

 tion of corrosive sublimate to which 5 per cent of glacial acetic 

 has been added. Eggs are left in this mixture for 4 or 5 minutes, 

 then rinsed in tap water and placed in 10 per cent formalin. 

 The formalin is changed after about one-half hour when it has 

 become slightly cloudy. This method if carefully handled brings 

 out in a most beautiful way the cell outlines of the ectoderm of 

 the yolk-sac (fig. 34) . The yolk remains rather transparent and 

 the mesenchymal cells may be observed beneath the clear cut 

 net-work formed by the ectodermal cell borders. This method 

 has been frequently employed by other workers and I have used 



