132 



CCELENTERATA. 



Externally, Cydippe is bi-plano-symmetric, for the plane passing 

 through the tentacles and their sheaths, called the coronal plane, differs 

 from that perpendicular to it, or the sagittal plane. Both planes, however, 

 divide the animal into symmetric halves. The gullet is flattened and 



Fig. 66. — Aboral View of Cydippe. (After Chun.) 



Aboral Sense-organ. 



Horizontal Canals. 



Tentacle. 



Comb. 



Fig. 67. — Adhesive Cells of 

 Cydippe. (After Hertwig.) 



Highly Magnified. 



Head. 



elongated in the sagittal plane, as in Actinia. Each of these planes 

 corresponds to two opposite per-radii. The stomach gives off, near the 

 gullet, four inter-radial canals which run horizontally outwards, each 



bifurcating into two ad-radials. Each 

 of these joins a long meridio7ial canal 

 running from oral to aboral end just 

 below each row of the combs. 



The aboral sense-organ consists of 

 a ciliated depression containing small 

 otoliths ( cf. Obelia ) and probably 

 governs the equilibrium of the ani- 

 mal. From it there pass eight 

 nerves down the eight rows of combs. 

 The coelenteron is here partially 

 divided, as in Actinia, into a central 

 gastric cavity or stomach and peri- 

 pheral nutritive, or vascular cavities. 

 The muscles are not represented, but 

 the gonads ( Cydippe is hermaphro- 

 dite) are situated on the walls of the 

 meridional canals. The mesogloea is 

 enormously developed and forms the 

 main bulk of the organism, filling the 

 space between ectoderm and endo- 

 derm. Nematocysts are not found in Cydippe but they have been 

 described in some members of the group. 



Stalk. 



