16 ALICE M. BORING AND RAYMOND PEARL 
so it is difficult to be sure of the sex. A comparison with sec- 
tions of just-hatched ovaries and testes seems to throw a little 
light on its nature. Even at this stage the testis has distinct 
tubules, but in the ovary, the oocytes are not yet enclosed in 
follicles, but the germinal epithelium has grown down into the 
stroma in solid cords (fig. 32). The appearance of the cortex 
is not unlike that of 1427. Sections of 1427 stained with Mal- 
lory’s connective tissue stain show no interstitial cells present, 
and also no lutear cells. ‘The probable conclusion then as to the 
internal structure of 1427 is that it is a female with an inactive 
gonad even less differentiated than in 1428. Development was 
probably checked by some pathological condition, of which the 
large tumor may be an index. 
The dissection of 1425 (fig. 18) is not very different from that 
of 1428 or 1427 just described, except for the absence of a vis- 
ible tumor. Sections show the posterior portion of the gonad 
to be filled with streaks of a secretion which resembles the 
substance of the tumor in 1429. This would indicate that it 
is in a similar pathological condition, although no separate 
tumor has been formed. Externally the reproductive organs of 
these three birds could scarcely be distinguished. Internally, 
however, the gonad of 1425 is more like that of 1428, in that 
the central portion is composed of tubules with distinct lumena, 
as shown in figure 22. There is no sign of any mitoses in any 
of the tubule cells, so they are probably of mesonephric origin, — 
that is, undifferentiated sex cords without any primitive germ 
cells. The peripheral portion has probably as in 1428 origin- 
ated from the germinal epithelium. There are no interstitial 
cells present in the stroma, and the number of groups of lutear 
cells between the tubules is less than in 1428. The presence 
of any of the latter clinches the diagnosis of this bird as a female 
arrested in development. The fewness of these cells may place 
it as more primitive than 1428,—that is, in between 1428 and 
1427. Unfortunately there is no record or photograph of ex- 
ternal characters to compare with the other two. 
The last of the Holland birds in the series, 1426, is distinctly 
different from the others in its structure. It has two repro- 
