520 • MARY B. STARK 



In the spring of 1916 an interesting mutation arose in the 

 form of a pigmented bar on the ventral surface of the last ab- 

 dominal segment of some of the larvae with tumors, as shown in 

 figure 10. Microscopic examination of a cross-section through 

 the bar revealed the fact that the pigment was deposited in the 

 large hypodermal cells of this segment, as shown in figure 11. 

 The bar was always perfectly shaped, as shown in figure 10, and 

 appeared only in larvae with tumors (fig, 12). An attempt 

 has been made to separate this mutation from the stock, but 

 this attempt has as yet not been successful. 



The tumor wherever developed is characterized by the pres- 

 ence of pigment, which increases excessively in amount with the 

 proliferation of the tumor cells. Pigment is normally present in 

 ganglion cells of the fly larva and, since the tumor usually de- 

 velops in cells closely associated with pigmented ganglion cells, 

 it may be possible that the pigment is derived from the ganglion 

 cells. The excessive production of pigment is probably due to 

 imperfect metabolism. Adami says: "It may well be that the 

 extraordinary deposit of melanin in melanotic tumors, far from 

 being a progressive acquirement, indicates a deficiency in the 

 disintegrative mechanism of the cell, whereby the normal, final 

 stage of colorless chromogen formation or of protein disintegra- 

 tion is not reached." May not the unperfect metabolism which 

 is the cause of the excessive production of pigment also be the 

 chemical stimulant productive of abnormal cell proliferation? 



METASTASES 



Mention has already been made of the presence of more than 

 one tumor in a larva. As many as fifteen have been observed in 

 some larvae. Most of these tumors were very small, however. 

 The smallest tumors are often found lodged within the dorsal 

 aorta. It may be that cells from the primary tumor have been 

 carried by the blood into the dorsal aorta where they develop 

 into secondary tumors or metastases. In a number of larvae, 

 tumors have been observed in all the regions described above 

 at the same time. In other larvae, the large primary tumor may 



