^Idyia^ ^I. roseola^ ^I. cyanthina^ [pg155] CLASS =CTENOPHORA= COMB-JELLIES These are delicate, free-swimming, generally spherical bodies, resembling jellyfishes in outline, transparency, and gelatinous consistency, but differing from them widely in the manner of locomotion. They are called "comb-jellies" from the rows of flat cilia, arranged like the teeth of a comb, which run in eight meridional lines over the surface. It is by means of these cilia that the animal moves through the water. The little paddles are worked in unison, in single lines, or each one of them can be moved independently, and they give the animal varying and peculiar motions. The /Ctenophora/ are nearly transparent, but have a prismatic coloring, caused by the waving cilia, and at night they are phosphorescent. They are widely distributed, being found in all seas. The mouth of the animal opens into a gullet which extends two thirds through the length of the body. On each side of the gullet is a vertical tube. The two tubes unite at the base of the gullet, and from there run as a single canal to the end opposite the mouth, and open to the outside through two excretory pores. From the base of the gullet, where the tubes unite, two other tubes extend laterally, which divide and subdivide in a horizontal plane, becoming eight in number, and connect at the surface with the lines of cilia; then, dividing, run in opposite directions to the poles of the spherical body. The animal derives its nourishment and air through this circulatory system. A nervous system is situated at the pole opposite the mouth, in a small area surrounded by cilia, in the center is an eye-speck, or lithocyst. [pg156] ORDER =CYDIPPIDA= GENUS ^Pleurobrachia^ [Illustration: /Pleurobrachia rhododactyla/, in motion.] ^P. rhododactyla.^ A transparent spherical body, one inch to one and a half inches in diameter, with eight combs or plates of flat cilia extending from pole to pole. At one pole is the mouth, like a slit, at the other a small area in the center of which is an eye-spot. From the body hang two tentacles, half a yard or more in length, fringed with cilia. The tentacles are very contractile and can be rolled up or expanded with great rapidity; they take graceful curves as the animal moves rapidly through the water. /Pleurobrachia/ has a pink tint, and prismatic colors play over it from the vibrating cilia. It is a beautiful and interesting creature to watch. Found along the shores of Massachusetts and Maine. ORDER =LOBATA= GENUS ^Bolina^ [Illustration: /Bolina alata/, seen from the broad side: /o/, eye-speck; /m/, mouth; /r/, auricles; /v/, digestive cavity; /g/, /h/, short rows of flappers; /a/, /f/, long rows of flappers; /b/, /n/, /x/, /t/, /z/, tubes winding in the larger lobes; /i/, base of gullet. About half natural size.]