MUSEUM OF COMPARATIVE ZOOLOGY. 175 
are lined with a vibratile plate. There is a pair of auricular appendages in 
each furrow, making four on both sides. 
The rudimentary tentacles are placed in a medial position in the furrow at 
the extremities of a diameter passing through the longitudinal axis of the 
mouth. They are club-shaped (Plate VILI. figs. 7, 8, 9), and bear in their re- 
duced condition small filaments or secondary appendages. These filaments are 
also found on the adjacent ridges of the body, extending in two rows, one on 
each side of the tentacle to the angle where the tubes from the “oral lappets ” 
and “auricular appendages” join (Fig. 10). The recess in which the rudimentary 
tentacles lie is closed on one side by a “hood,” d, Plate VIII. fig. 8. The tentacle 
springs from the body walls, and is affixed by one end and by a part of the 
lateral walls. In the adult the tentacle rarely projects beyond its socket. Its 
secondary appendages, however, are often extruded beyond the rim of the hood 
which shields the club-shaped tentacle to which they are affixed. The socket 
in which the tentacle lies, and one wall of which is made by the “ hood,” is the 
diminutive representative of the tentacular socket of Pleurobrachia. Scattered 
pigment cells of crimson colorin the base of the tentacle may represent a former 
ocellus. On either side of the base of the tentacle, Plate VIII. fig. 7, 8, a, the 
socket is continued into recesses not unlike the sense organs called * Riech- 
grübschen ” in the bell margin of Cyanea. 
The course of the lines of comblike swimming plates differs but little from 
that of the same structures found on the surface of the body in other Cteno- 
phore. Thereare eight rows of combs, four of which are much longer than the 
remainder.’ The modifications in their length are due to the abnormal develop- 
ment of the oral lappets. The rows of vibratile combs, which are situated on 
the same hemispheres from which the lappets are suspended, are much longer 
than those which lie in the furrows between theselobes. Isolated single combs 
from front and side are shown in Plate VIII. figs. 12, 12%, These combs retain 
their power of motion even when separated from the jelly-fish, and are often 
found rolled into a spherical ball, which is kept in rotation for a considerable 
length of time by their combined motion. 
With the exception of eight small vessels passing along the upper surface of 
the bell to the locomotive flappers, there are in Mnemiopsis no tubes which take 
origin from the upper end of the “funnel” near the otocyst. All the tubes 
arise from the lower extremity of the * funnel" just at its union with the upper 
end of the stomach, and not from the other extremity, upon which the otocyst 
is situated. The “funnel” itself is very short, but is well marked. From the 
lower end of the funnel arise six tubes, four of which by subsequent subdivision 
form the tubes, which lie under the locomotive flappers, while the remaining 
pair extend to the region of the mouth, each of the latter passing into a tenta- 
cle, b, Figs. 7, 8. The appearance of these tubes in the young Mnemiopsis, 
when they closely resemble each other, is shown in Fig. 8. 
The edge of the “auricular appendages ” has fastened to it a vibratile plate, 
which extends, without break, from the base on the side turned to the medial 
line, to the angle which the rim of the oral lappets makes with the body of the 
