354 PROFESSOR E, RAY LANKESTER. 
may be best understood from the figure (Pl. XX, fig. 8, p 2), 
and from the similar structure more definitely developed in 
the thoracic appendage (fig. 7 a.). I am not able to suggest 
what may be the significance of this lobe and notch, which 
has not been hitherto noticed by those who have described 
Apus, but it in some degree suggests a comparison with the 
peculiarly modified lobes on the first thoracic foot of the 
male Limnetis brachyurus (as described by Grube, Wieg- 
mann’s ‘ Archiv,’ 1853). 
The sub-apical lobe is relatively small, the flabellum and 
bract similar to those of hinder appendages. 
First thoracic foot.—This appendage is more strikingly 
modified than any one of the locomotor series, excepting the 
oostegopods, the remarkable feature being the elongation 
and jointing of the four middle endites in the form of fila- 
mentous flagella. The axis or corm of this appendage is 
divided into four successive segments, which are marked in 
the figure respectively Aw, Ax, Axv®, Ax* (Pl. XX, fig. 7). 
These segments are movable upon one another, the chitinous 
cuticle being soft so as to form an “arthrodial membrane ” 
between the successive joints. This is the only one of the 
truncal series of appendages (those following the oral appen- 
dages) which presents four joints to the corm, whilst the 
second thoracic foot is the only other appendage of the 
truncal series which presents a joint in the corm at all and 
in it only two segments exist. <A different structure is 
assigned by Professor Huxley to the corresponding limb 
and to the thoracic limbs generally of Apus glacialis, but 
it seems possible that the coxopodite, basipodite, ischiopodite 
and the endopodite with four joints recognised by him in that 
animal, are due to an interpretation of parts identical with 
those of Apus cancriformis, which differs from the interpre- 
tation here given. I must refer the reader for his views to 
the description and figures given on pp. 280, 281, of the 
‘Anatomy of Invertebrate Animals.’ 
The proximal or basal segment of the corm of the first 
thoracic limb of Apus cancriformis supports one endite, the 
gnathobase (£n'), which is quadrangular in outline and pro- 
vided with strong sete as in the other thoracic limbs. The 
second segment (Az”) supports a single endite, which is short 
and of filamentous form, with ten joints or annulations of 
the chitinous cuticle. These annulations in the present and 
other filamentous endites are not complete, but are developed 
only at the sides of the filament, leaving a continuous band 
of non-annulated chitinous cuticle mesially between the 
two series of half-rings ; and moreover, the half-rings do not 
