35 
of one, two or three, sometimes five, and. they cannot at all be 
said to be placed radially. 'Thus Pl. 13, fig. 6 of the »Panamic Deep 
Sea Echini” shows only one of them radially placed, the two 
others being decidedly interradial in position. We may then safely 
drop the idea of a homology between the outer anal plates of 
Cidarids and the infrabasals of Crinoids. It is evidently simply a 
consequence of the fact that there is more room left in the corner 
between each two genital plates that a more prominent anal plate 
is generally found here. 
It should further be pointed out that there is no indication 
of any anal plate ever breaking up to form several smaller plates, 
as suggested by Dåderlein in the sentence quoted above (p. 31). 
The plates are seen to be each formed separately. 
The Echinothuridæ, with their characteristic large anal area, 
covered by numerous small plates, do not beforehand convey the idea of 
a single plate covering the anal area from the first. Unfortunately 
very little is known regarding the development of their anal plates; 
upon the whole the young, postembryonal stages are not known of 
any Echinothurid as yet, the youngest specimens known being 3 
mm in diameter. A. Agassiz (Revision of Echini, p. 273. PI. 
II. c. figs., 1—5) mentions and figures a specimen of that size, 
which he refers to ,,Asthenosoma" hystrix. He gives, however, 
no description of the apical system of the specimen, so it is of no 
interest in this connection (— quite apart from the fact that its 
identification is very uncertain —). The ,,Ingolf"-Expedition col- 
lected several young specimens of Phormosoma placenta (Sigsbei), 
the smallest of which were 3 mm in diameter. In the Part Il 
of my work on the Echinoidea of that Expedition I have figured 
(p. 24, fig. 1) the apical system of such a specimen, The anal 
area is seen to be covered already by a considerable number of 
plates; nothing here points towards the existence of a primordial 
central plate. The figure is reproduced in Fig. 3. 
In the ,,Panamic Deep Sea Echini", p. 75, Agassiz says 
that ,,we may be justified in assuming that the anal system is in 
3% 
