154 



LOWER IN VER TERRA TES. 



rudimentary. Into the intestine opens a duct which divides in two main branches. These 

 branches subdivide into numerous follicles, the whole forming what is supposed to be the 

 liver, since it contains a bitter fluid like bile. The nervous system consists of a nerve 

 which runs, as a longitudinal ridge, along each ambulacral groove, and of a ring around 

 the mouth. At the end of each arm a rudimentary eye, continuous with the ambulacral 

 nerve, is placed at the end of a modified tentacle. The water system consists of a 

 canal running the entire length of each arm. This canal is placed in the angle foimed 

 by the ambulacral plates, and is thus external to them. It is separated by a strong 

 partition from a second canal which intervenes between it and the nervous band which 

 forms the bottom of the ambulacral gi-oove in the living animal. This lower canal. 



Fig. 135. — Bipinnaria of star-flsh ; am, rudimentary 

 ambulacra ; i, intestine; o, anus; 03, (esophagus; s, 

 stomach; w, water tubes. 



Fig. 136. — Later larva, with star-flsli (orraiug ; m, 

 mouth: ab, aboral portion of star-flsh. 



which is itself divided into two halves, is called the ambulacral neural canal, and com- 

 municates with a circular canal around the mouth. From opposite sides of the 

 ambulacral canal of the water system, short branches pass up between the ambulacral 

 ossicles to the ampullae, which are sacs with muscular walls lying above the ambulacral 

 l^lates, and within the cavity of the arm. Each ampulla communicates with a pedicel 

 or sucker by the pores in the ambulacral plates, as before described. The cavity of the 

 body and rays is filled with a watery fluid containing corpuscles, evidently represent- 

 ing the blood of higher animals. Pores, by which water can enter the body cavity, 

 are often i^resent upon the aboral aspect of a star-fish. 



The sexes are distinct, but can only be distinguished by a microscopic examination 

 of the glands, which are situated on each side of the interior of the arms, or at the 

 junction of the body with the rays. As the plates which enclose the base of the arms 



