533 



CTENOPHORA ; CTDirPE. 



in some species of the genera Lizzia and Sarsia, belonging to the 

 naked-eyed group, young Medusae are produced from buds 

 formed either from the stomachal peduncle or from the bases 

 of the tentacles ; whilst in a few species, one of which is the 

 common Pelagia noctiluca of the Mediterranean, it has been 

 found that the ova produce Medusas directly, without the in- 

 tervention of any polypoid form. 



ORDER III. CTENOPHORA. 



1191. Of the Order Ctenophora we have an interesting ex- 

 ample in the little Cydippe, which is often abundant on our own 

 coasts. This animal is of a nearly globu- 

 lar form, sometimes a little elongated at 

 the two extremities, and about three- 

 fourths of an inch in length. It is com- 

 posed of a delicate jelly-like substance, 

 strengthened by eight bands of somewhat 

 firmer texture, which run like meridian 

 lines from pole to pole. These bands are 

 covered with rows of large cilia, arranged 

 side by side, so as to form narrow plates 

 of a fin-like character. There are, in the 

 most common species, from three to seven 

 cilia in each row ; and about twenty rows on each ridge. The 

 whole ridge is not unlike the paddle-wheel of a steam-boat ; but 

 the motion is given by the vibration of the separate floats, and 

 not by the revolution of the whole. Over these floats the animal 

 has evidently complete control; it can retard or stop their move- 

 ments at pleasure ; and arrest the play of one, two, or more rows 

 whilst the remainder continue in rapid vibration. By these 

 means it is capable of swimming through the water with consider- 

 able activity, and of changing its course at will. The animals 

 themselves are of a bright faintly-blue aspect; and the cilia 

 present vivid iridescent hues when in motion. The mouth 

 is situated at one of the poles of the globe, and it is always di- 

 rected forward when the animal is in motion. It is a wide en- 



TIG. 726. CYDIPPE. 



a, a, tentacula ; b, mouth ; c, 



termination of intestine. 



