A STUDY OF SOMATIC CHROMOSOMES. 33! 



definite size relations among the chromosomes in the germ cells, 

 and these size relations can be followed out successfully in the 

 various tissues of the body. 



This series of investigations was taken up at the suggestion 

 of Prof. E. G. Conklin, and I wish to express my gratitude to 

 him for his interest in and helpful criticism of these investiga- 

 tions. I am also indebted to him for the use of his slides on the 

 spermatogenesis of Anasa. 



MATERIAL AND METHODS. 



The eggs of Anasa tristis in various stages of development 

 were obtained in abundance on the leaves of squash plants 

 during the months of July and August. The method of fixation, 

 which gave the best results, was that of Carnoy and Lebrun. 

 This fluid consists of equal parts of absolute alcohol, chloroform, 

 and glacial acetic acid, with the addition of mercuric chloride 

 to saturation. Eggs were well fixed in this fluid in from fifteen 

 to twenty minutes. From this fluid the eggs were transferred 

 to iodized 95 per cent, alcohol for twelve to eighteen hours, and 

 were then preserved in 80 per cent, alcohol. The eggs are sur- 

 rounded by an extremely tough chorion which must be removed 

 before sectioning. 



Larval ovaries were fixed for several hours in Flemming's 

 strong solution. This same solution was also used in making 

 preparations of the testes. 



Sections of both the sex glands and the eggs were cut 7-10 

 micra in thickness. Owing to the presence of the yolk in the 

 eggs, which becomes somewhat brittle after fixation, it is often 

 of advantage to separate the embryo from the yolk before em- 

 bedding, though this tendency of the yolk to crumble may be 

 obviated to a certain degree by the addition of a small amount 

 of crude rubber to the stock solution of paraffin. 



The stain employed in all cases was Heidenhain's iron-haema- 

 toxylin, with or without a counter-stain of erythrosin. The 

 value of a counter-stain is extremely doubtful, and perhaps the 

 best preparations were obtained by a long immersion in the 

 haematoxylin, which stains the chromosomes black but leaves 

 the cytoplasm a light gray or almost colorless after destaining. 



