276 J. T. PATTERSON AND H. L. WIEMAN. 



The worms were killed in the mixture heated to 50 C. and left 

 for one and one half hours. The eggs were treated with the 

 cold solution for about an hour. Excellent fixation was obtained, 

 and the material proved very favorable for cytological study. 



When the eggs were laid on the glass, they were allowed to 

 remain until 80 per cent, alcohol was reached, and then carefully 

 taken off with a sharp scalpel. An entire string may be removed 

 in this way without losing or injuring a single egg. 



The adults and eggs were embedded and cut in hard paraffin 

 (60 C.) to which sufficient quantity of a rubber-asphaltum- 

 paraffin mixture was added to produce a light amber shade. 

 Sections of 5, 7 and 10 micra thickness were cut without difficulty. 



Heidenhain's iron-alum-haematoxylin with orange G gave 

 very good results, but the method was in all cases checked by 

 staining parts of series with safranin and Lichtgriin. 



II. FORMATION OF THE SPINDLE. 



The nucleus of the egg has a very characteristic appearance 

 throughout the growth period. A coarse reticulum containing 

 varying amounts of chromatic material at its nodal points, 

 depending upon the degree of maturity of the ovum, and a large 

 spherical basic-staining nucleolus are always present (Fig. i). 



Fig. 2 shows an early stage in the prophase of the uterine 

 spindle, in which the chromosomes are forming at various points 

 in the reticulum. Our preparations clearly show that the 

 entrance of the spermatozoon into the egg is the stimulus which 

 initiates the process, and that uterine eggs in which a careful 

 examination fails to reveal the presence of a sperm invariably 

 have the nucleus in the resting condition. Owing to the hypo- 

 dermic method of insemination (Wheeler, '94) all the tissues of 

 the body at this time are filled with spermatozoa which finally 

 work their way to the uterus where they penetrate the ova. 

 In the impregnated ovum the head of the spermatozoon stands 

 out very distinctly as a deeply stained sickle-shaped rod, sharply 

 pointed at one end, so that its presence can be easily recognized. 



In Fig. 3 the chromosomes are fully formed in a group about 

 the nucleolus which at this time stains very faintly. The 

 nuclear membrane, though still intact, is somewhat wrinkled 



