102 J. Thomas Patterson, 



It is not necessary to enter into an extensive discussion of the 

 literature on the subject of the early development of the hen's egg, 

 for the several papers touching on this subject are well known. 

 The studies of Duval, '84, have, perhaps, received more attention 

 than those of any other investigator, and yet it has been demon- 

 strated that his fundamental conclusions are incorrect, and that 

 he was probably misled in his interpretations through the use of 

 pathological material (Kionka, '94; Barfurth, '95; Schauinsland, 

 '99; Patterson, '09). Kionka, '94, although figuring stages through- 

 out the greater part of the period to be considered in these studies, 

 does not give us a good idea of the character of the very early 

 cleavages. I^either of these workers, nor any one of the others who 

 have investigated these stages, has had anything like a complete 

 series from which to draw his conclusions; consequently it is not 

 surprising to find that the majority of the interpretations do not 

 accord with the principles of vertebrate development, and that the 

 more fundamental points are obscure. 



The recent discovery by Guyer, -'09, of an "accessory chromo- 

 some" in the male germ cells of the chicken lends unusual interest 

 to the study of fertilization in the hen's egg, for it ought to be 

 possible to demonstrate from the study of the mitoses of the super- 

 numerary sperm nuclei whether or not such nuclei are dimorphic. 



It was the writer's intention at first to publish the entire his- 

 tory, from ovulation to laying, in a single paper, but the slow 

 rate at which material naturally accumulates makes it desirable to 

 publish the part already completed; the remaining parts, one on 

 maturation and fertilization, and the other on late cleavage and 

 gastrulation, will appear later. 



II. Methods. 



Since the methods employed are essentially the same as those 

 used in handling the pigeon egg, they need be mentioned but briefly 

 here. The picro-sulphuric-acetic mixtures, which were found to be 

 so excellent for fixing the pigeon egg, do not work well, for they 

 render the yolk too hard. The picro-acetic fluid, however, although 

 not entirely satisfactory, gives fairly good results. Por preparing 



