THE GONADS OF THE FOWL 99 



tually succeed in penetrating into the veins but many of them 

 are phagocyted and digested by the endothelial cells. The phago- 

 cytosis of granulocytes by the endothelium is not so common 

 and may be due to their lessened wandering capacity. 



In degenerating blood-vessels the contents are also phagocyted 

 by the endothelium, whose cells increase considerably in size 

 after engulfing a considerable number of erythroblasts and other 

 cells. It is possible that also the ordinary mesenchyme cells may 

 contribute to the resorption of the granulocytes, but no clear 

 cases of this process could be found in the slides. 



THE ORIGIN AND TRANSFORMATIONS OF THE SMALL 

 LYMPHOCYTES 



In contrast with the accidental occurrence of stages in the 

 formation of the granulocytes, the small lymphocytes are a nor- 

 mal constituent of the gonads, both in the late embryos and in 

 mature birds. They have been regarded as connective-tissue 

 cells by Miss Boring ('12). According to this investigator, 

 the connective tissue in the adult bird is made up of cells which 

 differ in the structure of their nuclei ; some of the latter are round 

 and stain deeply, while others are oval or elliptical in outline. 

 Miss Boring regards this difference in the shape of the nuclei as 

 due to mechanical pressure conditions and states that "it is 

 possible to form a complete series of nuclei ranging gradually 

 from the typical elliptical connective tissue nuclei to the round 

 undifferentiated nuclei" ('12, p. 150). Cells similar to the ele- 

 ments with round nuclei described by Boring were abundant 

 in the gonads studied by the writer. While some of them are 

 undifferentiated mesenchyme cells, there can be little doubt that 

 the cells with deeply stained nucleus do not belong to the con- 

 nective tissue. Their morphological characteristics and origin 

 in the lymphatic nodules clearly show that they are small lym- 

 phocytes. 



The small lymphocytes begin to appear in the gonads and 

 adjoining organs after the fifteenth day of the incubation, gradu- 

 ally increasing in numbers until they form one of the normal con- 

 stituents in the adult gonads. They show their typical structure, 



