58 A. FRANKLIN SHULL. 



pairs separate into their components, each group proceeding to 

 the end of the spindle. In this late anaphase the cell appears 

 to remain until the egg is laid, for out of many specimens none 

 was found in later stages. 



NUMBER OF CHROMOSOMES. 



The tendency of the chromosomes to adhere to one another 

 in masses has rendered the determination of their number 

 difficult. Fortunately in my material a number of specimens 

 appear to agree in the number, and this is the largest number 

 found. In such specimens the chromosomes are of approxi- 

 mately uniform size, while in cells showing smaller numbers 

 some chromatin masses are nearly always distinctly larger than 

 others, indicating that the larger bodies are probably compound. 

 From a study of this material I conclude that the diploid number 

 of chromosomes is 12. In female-producing parthenogenetic 

 eggs, the best stage for counting the chromosomes is just before 

 or during the formation of the equatorial plate, because the 

 chromosomes are then well-defined, and are not so crowded as 

 later in the equatorial plate. Such a stage is represented in 

 Fig. 2. 



The chromosomes of the male-producing egg can be counted 

 fairly well at several stages. As in the female-producing egg, 

 one favorable stage is just before the formation of the equatorial 

 plate. In the equatorial plate the chromosomes can also be 

 counted, in these eggs, because the chromosomes unite in pairs, 

 hence there is a smaller number of discrete objects, and they are 

 not so crowded. Figure 3 shows distinctly six pairs. In this 

 figure the equatorial plate is viewed obliquely, and the pairs 

 are not at the same level, a fact not shown in the drawing. In 

 Fig. 4 there are six bodies, of which three show signs of bivalence. 

 The others may be bivalent, but appear single because viewed 

 from the end of the spindle. In late anaphases of the male- 

 producing egg the chromosomes are always crowded. Five 

 chromosomes can usually be recognized, but some specimens 

 show six. From the existence of six pairs on the equatorial 

 plate, I conclude that the number must be six even where only 

 five can be recognized. The late anaphases which are favorable 



