82 



SYSTEMATIC ZOOLOGY 



derives its name. Most of the Ctenophora possess two tentacles 

 which are retractile, and are inserted in pockets on opposite 



TTllh, 



Km;. 69. Hormiphora (Cydippe) plumosa. A, lateral aspect; B, aboral 

 aspect. Natural size; from the Mediterranean Sea. /'.tentacle; nith, 

 mouth; s.pl, swimming plates; /.tentacle. (After Chun, from Parker 

 and Haswell's Manual.) 



sides of the bodv. The mouth is at one pole of the animal, 

 and at the opposite or aboral pole is a sensory area in the 



center of which lies an otocyst. Nematocysts 

 are absent in the Ctenophora, but there are 

 cells, the adhesive cells, occurring on the 

 tentacles, which serve essentially the same 

 purpose ; thev have a hemispherical adhesive 

 surface, and a slender contractile stalk (Fig. 

 71). The mouth opens into an elongated 

 oesophagus lined with ectoderm, and termi- 

 nating in the central portion of the ccelenteron, 

 which here consists of several branching tubes, 

 of which the most important terminate in me- 

 ridional tubes, which lie just beneath the bands 

 of vibratile cilia. On these meridional tubes 

 lie the germ-glands containing on one side of 

 each tube, ova, and on the other, spermatozoa, 



FIG. 70. Idyia rosei 'la. 

 Lateral HSpect, halt 

 natural size, a, anal 

 opening; b, lateral tube ; 

 i i! cular tube ; d, e,f, 

 g, /;, rows of paddles. 

 ( After Agassiz, from 

 Parker and Haswell's 

 Manual.) 



