60 CCELENTERATA AND 



regularly distributed. Certain sea-cucumbers and brittle- 

 stars have feet destitute of suckers. 



The nervous system is exposed to the water in star- 

 fishes, but is covered by a series of plates in brittle-stars 

 and sea-urchins and is internal in sea-cucumbers. Eye- 

 spots are found at the ends of the rays in star-fishes ; in a 

 ring about the aboral region in sea-urchins and are want- 

 ing in Crinoids and brittle-stars and possibly in sea- cu- 

 cumbers. Special organs of smell exist on the under or 

 oral surface of the star-fishes as shown by physiological 

 studies. Otocysts are known in deep-sea genera. 



The ovarian openings lie in the angles of the rays or in 

 the vicinity of the mouth in star-fishes ; in a circle about 

 the aboral region in sea-urchins and on the lateral cirri in 

 Antedon. In brittle-stars there are four broad openings 

 on the side of the disk, called by some genital slits. By 

 many naturalists these are regarded as respiratory open- 

 ings. Holothurians generally have a single sexual open- 

 ing near the mouth. 



A madreporic body or convoluted prominence is well 

 marked in star-fishes and sea-urchins and hidden or want- 

 ing in snake-stars and sea-cucumbers. 



The sexes are ordinarily separate. Some star-fishes, 

 snake-stars and the sea-cucumbers are probably hermaph- 

 rodite. The Echinodermata have a direct or indirect de- 

 velopment, and some are viviparous. 



The Echinodermata of our coast are divided as follows : 



Free Crinoidea. 



Body with pinnate rays, with jointed cirri on the aboral 

 region. 



Aster oidea. 



Body stellate or pentagonal, with an aboral and oral 

 region, the latter only crossed by five or ten double radial 



