THE HOLOTHURIOIDEA 



233 



retractor muscles ; tentacles digitate Molpadia, Cuvier. B. Retractors 



absent or rudimentary Eupyrgus, Liitken ; Haplodactyla, Grube ; 



Caudina, Stimpson ; Trochostoma, Dan. and Kor. ; Ankyroderma, Dan. and 

 Kor. (Fig. I. 10). 



vim- 



1. Left side view of Synapta digitata, Mont. 



2. The same opened up to the right of the median " dorsal " line. 



3. Diagram of the water-vascular system of S. digitata illustrating the Paractinopod plan. 



4. Ciliated urns; and 



5. Transverse section through the radius and otocysts of S. digitata. (After Cuenot.) 



(>. Anchor and anchor-plate of .S'. digitata. 



7. Wheel of Myriotrochus Rinkii, Steenstrup. (After Danielssen and Koren.) 



<r, anus ; on, anchor ; an.p, anchor-plate ; b.?r, body-wall ; c.c, circular canal ; c.f, coelomic 

 epithelium ; c.m, circular muscles ; c.u, ciliated urn ; d.mcs, dorsal mesentery ; e.s, epineural 

 sinus ; g.p, genital pore ; i, intestine ; l.g, left gonad ; m, mouth ; mes, mesentery ; n, nerve ; 

 o.c, otocyst ; oe, oesophagus ; o.l, otolith ; ps.c, pseudhaemal canal ; r, rectum ; r.g, right gonad ; 

 r.mcs, right mesenterial fold ; r.n, radial nerve ; s.c, stone-canal ; st, stomach ; t, tentacle ; t.c, 

 tentacle canal ; v.l.m, median ventral longitudinal muscle. 



The Molpadiidae are rounded forms, with generally a tapering, tail- 

 like, posterior end. The tentacles are simple processes, or of lobed or 

 digitate shape. Their ampullae are large and free, except in Eupyrgus (T). 

 There are no podia, unless they be represented by the anal papillae. As 



