APPEN DAGES AND NERVOUS SYSTEM OF APUS CANCRIFORMIS, 351 
new development or recurrence of ancestral conditions of 
form. In Pl. XX, fig. 12, an abnormal specimen of the 
fortieth appendage, right side, is drawn. The abnormality 
consists in the development of a second flabellum nearer the 
base of the corm than the first, and this is accompanied by 
an almost complete reduction of the bract. The additional 
flabellum is much smaller than the normal one, but has a 
similar form, and is supplied with a muscular slip. 
Thoracic appendages, or appendages at and in front of the 
genital apertures and behind the specialised oral appendages. 
—It will be most convenient to examine these appendages 
by proceeding from behind forwards. 
Oostegopods.—The pair which are attached to the segment 
in which the genital ducts open in female specimens of Apus 
are, as is well known, modified so as to form receptacles for 
the eggs. Inthe males, as shown by Brauer (‘ Wiener Sitz- 
ungsber,’ vol. lxix), the appendages of this segment are in 
nowise different from those of the segments immediately in 
front of them. 
The oostegopods, or brooding-legs (as the eleventh pair of 
the thoracic appendages may be called), present the following 
peculiarities as compared with the appendages in the region 
posterior to them. The gnathobase and four succeeding 
endites are normal (Pl. XX, fig. 10), and resemble those of 
the next posterior appendage (PI. XX, fig. 11), but the sixth 
endite is greatly modified. It is expanded and confluent with 
the subapical lobe (p). The subapical lobe is widely pro- 
duced in the form of a hemispherical cup. On to this ex- 
pansion the flabellum (F/) fits as a lid—an emarginated 
aperture being formed posteriorly to its short peduncle by 
the notching of its border (Pl. XX, fig. 10, ov). 
The great development of the subapical lobe and modi- 
fication of the flabellum seems to have entailed an atrophy 
of the bract (Br), which exists in a rudimentary filamentous 
condition (compare the abnormal appendage drawn in 
fig. 12). 
The general form of this appendage has been described by 
many previous observers, and the relations of its parts to 
those of neighbouring appendages correctly pointed out. The 
correspondence of the immovable, cup-like portion, developed 
from the axis or corm, with the conjoined sixth endite and 
subapical lobe (which is relatively large in the next following 
appendage posterior to it, fig. 11), has not, however, been 
insisted upon. Zaddach correctly identifies the movable lid 
with the flabellum, and figures the limb in an immature con- 
dition with the rudimentary bract present. He states that 
