HYDROZOA. 



G5 



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. Hormipltora pUimosa* 

 {Fig. 2(j) 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 mouth 

 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 



Case 3, 

 Upright part. 



rM. ^t 



B 



Cestus veneris, a, adult, b, young, mth, mouth ; <, tentacles; Z<, lateral 

 tentacles ; spl\ one of the four short rows of swimming plates ; spP, 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. 



Bero'e 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. 



