!1S G. E. COGHILL 



Figures 28 to 54 were drawn with the aid of the Bausch and Lomb drawing 

 apparatus at a magnification of 400, reduced to 200 in the figures. They are taken 

 from four embryos, designated in my series of preparations as 467, 473, 449 and 444. 

 These embryos are taken as type specimens, respectively, of the four physiolog- 

 ical stages that are described in the paper, namely, the non-motile stage; the early- 

 flexure stage, the coiled stage, and the early-swimming stage. The methods of 

 preparation of these four specimens were as follows : 



467, Non-motile stage; fixation in corrosive-sublimate-acetic-acid mixture; 

 stained in Delafield's hematoxylin and acidulated orange G; transverse plane; 10 ju. 



473, Early-fiexure stage; fixation in corrosive sublimate-acetic acid mixture; 

 stained in alum carmine and Lyon's blue; transverse plane; thickness, 10m- 



449, Coil reaction stage; same fixation; stained in cochineal and Lyon's blue; 

 transverse plane; thickness, 10/^. 



444, Early-swimming stage; same fixation; stained with Boemer's hematoxy- 

 lin and acidulated orange G; transverse plane; thickness, 10 m. 



