20 
W. F. PURCELT,. 
fit varying ang-les. The first or medial furrow [ f. 1) is 
always much the deeper and extends from near the medio- 
posterior angle of the base of the appendage in a latero- 
distal direction. As a rule when the posterior face of the 
appendage is strongly inclined, the furrow takes a more 
transverse direction and does not then reach the distal 
surface (as in figs. 8 and 14), but when the posterior face is 
less inclined, the furrow takes a direction more nearl}- 
parallel to the axis of the appendage, extends right up to 
tlie distal surface of the latter, and comes to be situated on 
its medio-posterior corner (fig. 10). In such cases, in fact, it 
is sometimes more on the medial than on the posterior side 
of the appendage. The second furrow (/. 2) appears 
almost simultaneously with the first, and is situated between 
the latter and the base of the appendag-e, so that its medial 
end terminates on the proximal side of the lateral part of the 
first furrow. It never extends right to the base nor to the 
distal surface of the appendage, and if produced medially 
would run proximally to the first furrow. 
Compared with the preceding stage the medial half of the 
appendage has developed considerably and is sharply set off 
from the body surface. Further, in its lateral part (fig. 8g) 
the anterior side has become much more inclined than in the 
preceding stage (fig. 7a), so as to be parallel to the slanting 
anterior wall of the pulmonary sac. In longitudinal sections 
through this part (fig. 8g) the appendage has the false 
appearance of being directed backwards, and this becomes 
still more marked in later stages (as for instance figs. 12 and 
IGc). That this appearance is deceptive and merely due to 
the pulmonary sac will be readily seen if it be remembered 
that fig. 8g is a section lying between the sections fig. 8f and 
fig. 8h, and fig. 16c a section between fig. 16a and fig. 16n. 
The main axis of the appendage remains in all cases at right 
angles to the body. 
Stages with three or more pulmonary furrows (stages 8 to 5). 
— I’lie third furrow ( /. 8, fig. 16) appears at the middle of 
the base of the posterior side of the appendage. It is 
