ECHINODERM MORPHOLOGY. 
325 
The observations of MetschiiikofF and Agassiz are quite in 
accordance with this fact. The former figures the apex of 
a young Starfish in which the madreporic plate is already 
formed, but is situated at the edge of the disc quite outside 
the circle of genital plates ; while Agassiz represents a 
young Starfish which shows the position of the madre- 
poric body immediately on the edge of the disc of the lower 
(i.e. actinal) side.^^ Somewhat the same is the case in the 
adult Ophiurids. Although developed on the dorsal surface 
of the larva the water-pore is usually on the actinal surface 
of the adult ; while in Trichaster it is neither abactinal nor 
actinal, but intermediate in position, somewhat as in the 
earlier stages of the young Starfish. 
In the same way the anus of the Starfish is at first upon 
the actinal side near the edge of the disc.” But as growth 
proceeds it moves towards the abactinal surface together with 
the water-pore. In the Crinoids, however, the position of 
the future anus is gradually shifted in the reverse direction, 
i,e. towards the actinal surface ; while the water-pore must be 
developed late, unless we are to suppose that it escaped the 
notice of both Gotte and of Wyville Thomson in the earliest 
larval stages. But whereas in the other Echinoderms it is 
developed very early, before the appearance of the actinal 
or abactinal plates, the rudiments both of these and of the 
chief organs of the Crinoid appear before it, and then it is 
only found perforating the “ seitlichen Randtheil ” of an 
oral plate. 
As far as the Crinoids are concerned, this is the chief 
evidence in favour of Ludwig’s views, but it is not complete 
even for this group. For while Rhizocrinus has five water- 
pores like some exocyclic Urchins, their openings are not in 
the persistent oral plates^ as they should be on Ludwig’s 
theory, which compares these orals to the genitals of the 
Urchins, because one of them in the larval Antedon is per- 
forated by the w’ater-pore. Further, the orals of the Crinoids 
have precisely the same relation to the water-vascular ring 
and to its tentacular apparatus surrounding the mouth as 
the five plates figured by Kowalevsky in the Psolinus larva. 
Ludwig will hardly deny that these last are orals, but not 
one of them is perforated by the water-pore. On the con- 
trary, it is separated from them by the whole length of the 
^ If the orals of Rhizocrimis are perforated by the water-pores, surely 
Ludvyig would have said so ; and I gather from his figure of the water-j)ore 
ill this genus that this is not the case (‘Zcitschr. f. wiss. Zool.,’ xxix, Taf. 
V, fig. 8). 
