BRIEF REVIEW OF THE SYSTEM OF LIFE. 



429 



into the arms ; mouth below, at center ; arms or rays with a groove on the lower side, 

 along which the locomotive suckers protrude through perforated plates ; eyes at the tips of 

 the arms. Ex., the Star-Jish, Fig. 442. 



4. Ophiuroids {Serpent- Stars). — Having a disk-like body with a star-shaped mouth 

 beneath, and long, jointed, flexible arms, which sometimes subdivide by forking, but never 

 bear pinnae, and have no grooves along the under side, nor eyes at the slender tips. The 

 viscera do not extend into the arms ; the ovarial openings are slit-like, between the bases 

 of the arms ; and there is no anal oi-ifice. The disk part is homologous with the whole of 

 an Asterioid. 



5. Crinoids {including Gomatulids) . — Like ordinary star-fishes in having flexible 

 arm^s or rays ; but the calcareous secretions of the rays and body constitute a series of 

 closely fitting solid pieces, and the viscera are confined to the body portion. The rays are 



435-444. 



436 ^t.^-^ *35^fM^(m 



Radiates.— Figs. 435-444. 1. Polyps : Fig. 435, an Actinia; 436, a Coral, Dendrophyllia; 437, a Coral of 

 the genus Gorgonia. 2. Hydrozoans : 438, a Medusa, genua Tiaropsis; 439, Hydra (x 8) ; 440, Syn- 

 coryne. 3. Echinoderms : 441, Echinus, the spines removed from half the surface (x J) ; 442, Star-iish, 

 Palaeaster Niagarensis ; 443, Crinoid, Encrinus liliiformis ; 444, Crinoid, of the group of Cystoids, Cal- 

 locystites Jewetti. 



often very much subdivided, and bear pinnse, in which the generative organs are situated. 

 The species are mostly fossil, and are among the earliest in geological history. A few 

 kinds still live in the ocean mostly below 20 fathoms, some at great depths. There are 3 

 tribes of Crinoids : — 



I. The Brachiates {Encrinites) . — Having a radiate structure, and arms proceeding 

 from the margin of the disk ; also generally a stem, consisting of calcareous disks, by 

 which, when alive, they are attached to the sea-bottom or some support, so that they stand 

 in the water and spread their rays, like flowers, the mouth being at the center of the 

 flower. Crinoids are represented in Fig. 443, Fig. 433, and Fig. 30 on page 58. The 

 second and third are living species from the West Indies, found at depths below 20 

 fathoms. The rays open out, when alive, and then the animal has its flower-like aspect. 

 The little pieces that make up the stem, looking like button-molds, are either circular, as 

 in Fig. 443 a, or 5 sided, as in Figs. 433 a, 5, c, d. Under the Crinidea fall the Comatnlce 

 (Antedon, etc.), which are free when adult, but have jointed cirri proceeding from the 

 back surface for attachment. 



