GERM-CELLS OF PHRYNOSOMA CORNUTUM. 



121 



conclusions, although differing from Dr. Allen's in details of 

 early distribution and period of migration, uphold his. 



My work was done on Plirynosoina cormituin Harlan, of cen- 

 tral Texas. The material was largely supplied from the collec- 

 tions of Miss Augusta Rucker ; I take this opportunity to express 

 my thanks to her, and also to Dr. Thomas H. Montgomery, 

 under whose direction this study was completed. 



The embryos were fixed in nitric acid, Zenker's fluid, and picro- 

 sulphuric acid, the last proving to be the most satisfactory ; the 

 sections were double stained with Heidenhain's iron hsematoxylin 

 and alcoholic eosin, and sections were made 6 micra thick. 



The most careful study was given to series No. 26 ; a stage 

 where the intestine is completely closed except at the region ot 

 the yolk-stalk which is i 5 mm. wide ; the allantois is well devel- 

 oped, and two visceral clefts have broken through. This was 

 compared with series No. 12, an embryo with five visceral clefts. 

 Each section was examined under an immersion lens, and the 

 number and positions of the germ-cells were tabulated. In ser- 

 ies No. 12, the peritoneum of the germ-gland anlagen is distinctly 

 thickened throughout the region of the mesonephros ; within 

 these thickenings there are found at intervals large rounded cells, 

 with clear cytoplasm containing yolk and large clear nuclei with 

 deep-staining chromatin granules. Two of these are drawn in 

 Fig. I ; the nucleus of the left germ-cell measures 6 micra and 

 5 micra in its diameters ; that of the right, 7 micra and 6 micra. 

 These were called typical germ-cells ; considering their appear- 

 ance and position, no other satisfactory explanation of their nature 



Series 12. 



Series 26. 



Series 27. 



'lateral to central 



nervous system 



Sclerotome "1 lateral to aorta — 

 within mesentery. 



.of yolk-stalk 



Mesothelium 



Germinal anlage 



Ectoblast 



T- . ui ,f of axial intestine — 



^"'°^^^^n of yolk-stalk 



Cavity of yolk-stalk 



Total , 



9 

 22 



4 



3 



44 



17 



one row of sec. 



17 



