212 RALPH DOUGALL LILLIE 



one hundred of sublimate-Muller being the proportion used. 

 The larvae were extracted three to six days in iodized alcohol and 

 preserved in 85 per cent alcohol. Imbedding was in paraffin, in 

 gelatin-paraffin (Weber, '14), and in celloidin-paraffin. 



Serial sections 5 n in thickness of the larvae up to 9-mm. body 

 length were made. From the later stages the mesonephros, liver, 

 pancreas, and heart were dissected out and sectioned alone. 



For stains Hansen's iron hematoxylin with eosin or orange G, 

 Dominici's jeosin-orange G-toluidin blue, Maximow's eosin-azure 

 II, and thionin were used, the sections being cleared in xylene and 

 mounted in xylene-damar. Wright's stain diluted with two parts 

 of water was also used, staining being sufficient in about ten 

 minutes, the differentiation being secured in alcohol rather than 

 in water. As controls and for comparison smear preparations of 

 adult blood and bone marrow were used. 



THE VENTRAL CELL MASS 



No discussion of the origin of this cell mass, whether ento- 

 dermal or mesodermal, will be made here, the evidence for its 

 mesodermal origin being deemed sufficient. In a larva of 2.5- 

 to 3-mm. body length it forms two plates on the ventrolateral 

 aspects of the yolk mass. It is distinguished from the latter by 

 the greater number of nuclei, the somewhat smaller size of the 

 yolk granules, and a line of demarkation, which, although not too 

 well defined, is nevertheless distinguishable. There is no strik- 

 ing difference in nuclear structure. 



This mass is apparently syncytial in character, at least, no 

 cell boundaries are evident by ordinary methods. I believe that 

 is largely due to the pale character of the cytoplasm, which is 

 greatly obscured by the large rounded or elliptical yolk granules. 

 The same indefiniteness of cell outline obtains in the yolk mass 

 itself. But occasionally polygonal cells are seen outlined by 

 pigment, and more clearly by the blue stained (eosin-azure II) 

 gelatin of the imbedding mass. These cells are rich in yolk, less 

 so than the yolk entoderm cells, their yolk granules being about 

 6 n long and half as broad. These granules stain readily with 



