38 MASS. EXPERIiMENT STATION BULLETIN 391 



intestinal loops were attached to each other by firm adhesions. The ovary was 

 inactive and the visceral organs otherwise normal. 



The histology of the tumor was somewhat variable. The bulk of the mass 

 was made up of sheetlike masses of moderate-sized oval or polyhedral cells with 

 rather pale, round nuclei (Plate IX, Figure 4). In some parts the cells assumed 

 a cuboidal form and arranged themselves in rows, and in other areas they were 

 compressed to a spindle form. Areas of hemorrhage and necrosis were found. 

 The visceral serosa was thickened by a fibrinous covering in which some organ- 

 ization had taken place. 



Melanoma 



As mentioned in the section dealing with epithe'ioblastoma, a small melanoma 

 was found at the base of the tongue in a bird which also had a foetal adenoma of 

 the thyroid. Both of these tumors were incidental findings in a bird killed for 

 examination because of laryngotracheitis infection. 



1. Case T 101. The bird was a 6-month-old female. The melanoma con- 

 sisted of a small, encapsulated mass situated in the loose areolar tissue on the 

 ventral surface of the h\oid bone at the base of the tongue. It attracted atten- 

 tion because of its black color. The tumor was round and somewhat flattened, 

 measuring 5 mm. in diameter and 2.5 mm. in thickness. Histologically it con- 

 sisted of a rather compact mass of cells which appeared to be arranged in the 

 form of a syncitium. The nuclei varied in size, but in general they were relatively 

 large, vesicular, and contained distinct nucleoli. There was a variable amount 

 of black pigment in the cytoplasm of the cells. In some cells this was arranged 

 in the form of very fine dustlike particles; and in others the granules were coarse, 

 in some instances entirely obliterating the cell structure (Plate VII, Figure 4). 

 In general the tumor did not appear to be actively growing and it may be re- 

 garded as a benign tumor. 



Embryonal Nephroma 



Embryonal tuniors of the kidneys of the chicken are usually composed of a 

 mixture of epithelial and connective tissue elements and probably arise as result 

 of a defect in development of the kidney. There were 21 cases of embryonal 

 nephroma in this series of tumors of the chicken, 11 of which were females and 

 10 were males; a sex ratio of 1 to 1. The average age at necropsy was 27.2 weeks 

 (the youngest case died at 7 weeks and the oldest case was killed for examination 

 at 50 weeks). Eight of the group were killed at an average age of 19.4 weeks 

 and the remaining 13 died at an average age of 32.1 weeks. These cases were 

 somewhat younger than those reported in the literature. For example, Mathews 

 (18) described a series of 12 cases, 9 of which were in birds between 9 and 24 

 months old. 



The tumor masses were all confined by either the capsule of the kidney or a 

 well-developed capsule of their own. The size and shape of the tumors varied 

 considerably (Plate X, Figures 1 and 2). In two instances, no tumor was ap- 

 parent at the time of necropsy and its presence was revealed only by histological 

 examination of the kidney. The largest tumor weighed 299 grams and had com- 

 pletely replaced the kidney. Embryonal nephroma was associated with cysts 

 of the kidney in four instances. The histological appearance of the cases was 

 likewise variable, although both connective tissue and epithelial constituents 

 were present in all. The variations were principally in the relative amounts of 

 these elements (Plate X. Figures 3 and 4). Keratinization and epithelial pearls 

 were found in si.x tumors, although in none was this process as well developed 

 as in the case described by Feldman and Olson (9). In one instance of a unilateral 

 mass arising from the left kidney, there were many areas of cartilaginous tissue. 



The embryonal nephromas were unilateral in 16 of the cases, affecting the left 

 kidney in 7 instances and the right kidney in 7; while in 2 cases the site was 



