136 Harry Lewis Wieman. 



The present paper embodies a study of important stages occur- 

 ring for the most part in the pre-maturation period of the germ 

 cells. Recent discoveries in chromosome behavior have brought 

 the reproductive cells of insects into considerable prominence; 

 but most of this work has been prosecuted along rather narrow 

 lines. The chromosomes are undoubtedly important elements, 

 but they are far from being the only factors to be considered in a 

 study of the mechanism of heredity. The cytoplasm, though long 

 neglected, is coming more and more to be recognized as of equal 

 if not greater importance in this regard ; and in the present under- 

 taking the so-called nucleo-cytoplasmic relationship has been 

 studied by following the morphological and chemical transform- 

 ations undergone by the cellular elements of the ovary and testis 

 during critical stages of development. 



The ovum offers a more extended field for observation than 

 the spermatozoan ; since spermatogenesis is a relatively simple 

 matter compared with the complex changes involved in the pro- 

 duction of a mature ovum.- As a result I have given more atten- 

 tion to the reproductive organs of the female than to those of the 

 male. 



To Professor CO. Whitman, at whose suggestion this work was 

 taken up, and to Professor W. L. Tower, who kindly supplied 

 me with material from his pedigreed stock, I am greatly indebted 

 for much valuable advice and criticism. 



Methods 



Two distinct methods of killing and fixing were followed de- 

 pending upon whether chemical or morphological differentiation 

 was the object sought after. Experience showed that Flemming's 

 strong solution was far superior to any other reagent for faithful 

 preservation of morphological detail; but the presence of osmic 

 acid greatly interferes with the action of stains employed in the 

 study of chemical changes. For the latter purpose I used a 

 saturated aqueous solution of picric acid to which sufficient 

 acetic acid was added to make a 10 per cent solution. This does 



