53 
natural thing would be to regard it as representing the genital 
2 alone, homologous to the madreporic plate of the ethmophract 
Amphisternata, and of the Echinoids in. general, only grown exces- 
sively (Fig. 18). That this is the correct view, 
is shown by the development of the plates of the 
apical and anal system. This development has 
been studied by Lovén, A. Agassiz and the 
present author, especially in Abatus cavernosus 
(and cordatus). In my work ,,The Echinoidea of . i 
j 6 Fig. 183. Apical 
the Swedish Southpolar Expedition" ”) (p. 75—78) system of 
the development of the apical system of Abatus  Macropneustes 
Pellati Cott. 
(From Lovén). 
cavernosus is treated at some length. It is shown 
that there is no central or suranal plate developed 
(cf. Pl. XVII, fig. 9); on the other hand a distinæct genital 5 is 
developed at the hind edge of the anal area. (Fig. 14). It is thus 
made certain that Lovén's view 
of the madreporite representing 
the genital 2 +- the central plate 
+ the genital 5 cannot be main- 
tammed. Also in Amphipneustes 
Koehleri Mrtsn. the same holds 
good, as shown by the young 
stage figured in Pl. XVIII, fig. 2 
of the work . quoted. In the 
light of the facts thus made 
known regarding the development 
Fig. 14. Apical system and sur- 
roundings of a young Abatus carver- 
nosus. The plates numbered 1,2..,5 Savernosus, the young stages of 
are the genitals, those numbered I, Echinocardium flavescens, Bris- 
II—V the oculars. (From. Th. 
Mortensen). 
of the apical system in Abatus 
aster fragilis, Hemiaster exper- 
gitus figured by Lovén (On 
Pourtalesia. Pl. XV. Fig. 173) and by the present author (,,Ingolf"'- 
Echinoidea. II, p. 98, fig. 17. Pl. XIII. Fig. 2), though already 
1) Schwedische Sidpolar-Expedition. Bd. VI. 4. 1910. 
