HYDROZOA. 
65 
to the exterior on each side of a centrally-placed “auditory” or 
balancing sense-organ. 
Some Ctenophorans are provided with a pair of plumose tentacles, 
which can be retracted into receptacles. Hormiphora plumosa* 
(Fig. 26) has a small pear-shaped body, the mouth being at the 
narrow end ; the eight rows of swimming-plates occupy about two- 
thirds of the length of the body ; a pair of long feathery tentacles 
can be emitted from two tentacle-sheaths, which open one on each 
side of the body not far from the aboral pole. 
Cestus veneris , or “ Venus’ Girdle ” * (Fig. 27), has a long band- 
shaped body, which may attain a length of several feet ; the month 
is in the centre of the lower border, and the gullet and stomach 
occupy quite a narrow .area in the centre of the band ; the eight 
Fig. 27. 
Cestus veneris, a, adult, b, young, mtli, mouth ; t, tentacles ; It, lateral 
tentacles ; spl 1 , one of the four short rows of swimming plates; spl 2 , one 
of the four long rows of swimming plates. (After Chun ; from Parker 
and Haswell’s Zoology.) 
rows of swimming-plates form an apparently continuous line on each 
edge of the upper border. The young Cestus is spheroidal, but soon 
becomes compressed in a vertical plane and lengthened out. 
Cestus swims mainly by the wavy and serpentine motion of its 
body. The small exhibited specimen shows the aboral border, with 
its apparently continuous rows of swimming-plates nearest the front 
of the glass. 
Beroe ovata * from Naples is in the form of a large sac with a 
wide mouth ; the cavity of the sac is, strictly speaking, the gullet, 
the stomach occupying only a small space at the base. 
Beroe ovata can alter its shape to a remarkable extent while 
swimming, being now V-shaped with widely-gaping" lips, now 
U-shaped ; the creature is extremely voracious, and can take into its 
F 
Case 3, 
Upright part. 
Case 3, 
Upright part. 
