SYSTEM AND SUrJlAlllJNAL BOOIKS IS THE SPARROW. 



'45 



possess large clear oval nuclei above described, but the sur- 

 rounding cytoplasm af)peara to lose its individuality, with the 

 resulting formation of syncytial masses or strands, in which 

 there is evident niitotic activity. Kohn (12) fi,i>ures snch strands 

 in the Rabbit. Streeter (13) considers this syncytial character 

 to be only transitory, and associates it with the period of migra- 

 tion. Conteui])oraneonsly with this migratory activity of nervous 

 elements the [)rimordia of the segmental arteries and veins are 

 being laid down. Thus in text-Iig, .3 we see that the endothelium 

 of the dorso-ln.teral angle of the aorta 1ms [)rolifei-ated to form 

 a distinct strand of cells, which will ultimately develop into a 



Text-figure 3. 

 s.c. 



A<Cc. 



Myt. 



s^c 



'Se^.Art. 



Transverse section of Sparrow embr3-o 15 (= 42-lir. chick), sliowing development of 

 segmental artery and migration of sympathetic cells (Si/.C), 



Ao. Aorta. C.E. Creloniic epithelium. Myt. Myotome. S.C. Spinal 

 cord. Sog.Art. Segmental artery. Sy^C Migrating sympathetic cells. 

 mc. Notochord. (Sp. 15, 3, 1, 1.) 



segmental artery. Similar vascular strands may be seen in other 

 sections arising from the cardinal veins. The nuclei of the cells 

 in these vascular strand.s are very irregular in shape, and theii' 

 <;ytoplasm is considerably lighter and less granular than that of 

 the nerve strands. In view of the fact that some authors have 

 been led to consider such strands as of nervous significance, we 

 venture to direct special attention to this difl'evenfciation. 



That the cells migrating from the dorsal ganglia are neuro- 

 blasts is confirmed by silver preparations of chick embryos in 

 which the ventral roots have not yet appeared, u6. of less than 



