9 8 
TH. MORTENSEN, 
(Schwed. Südpolar-Exp. 
and younger. The largest specimens from the marsupium correspond very nearly 
to the stage of Abatus cavernoszis described above (p. 76 PI. XVII. Fig. 9); the 
apical system is not quite so far on in its development, the anal plates have only just 
begun to appear; the genital plate 5 is distinct. Upon the whole it corresponds 
closely to that of A. cavernosus. Both mouth and anus are closed as yet. The 
terminal suckers are rather conspicuous. There is no trace of a peripetalous fasciole, 
and, since in Abatus cavernosus the fasciole is already distinct in specimens of a 
corresponding stage, it seems evident that a fasciole is never developed in this form. 
— It is, however, desirable that somewhat larger young ones should be examined 
for settling this important question definitely. It can scarcely be doubted that the 
further development is quite in accordance with that of A. cavernosus , with the ex- 
ception alone of the absence of a fasciole. — Pedicellariæ 
have not appeared as yet in these young specimens. 
The specimen next in size is 7.5 mm. long, 7 mm. 
broad and 4.5 mm. high (PI. XI. Figs. 2, 4), its shape 
being thus, upon the whole, already like that of the grown 
specimens. The periproct has almost its definite place, 
only slightly more to the abactinal side. The ambulacra 
are as yet simple, without any indication of the later peta- 
loid condition; the pores are single. The apical system 
(Fig. 28) is interesting in showing the same feature as the 
type specimen of A. Lorioli , viz. the madreporite being 
separated from the right anterior genital plate by a trans- 
verse line, resembling thus a real central plate — though 
I do not mean to maintain its homology with the central 
(suranal) plate of Salenia , Echinus etc.; it reaches some- 
what beyond the posterior ocular plates, even a little more so than in the grown 
specimens (cf. Figs. 26 — 27). Also on the left side a small plate appears to have 
been separated from the madreporite, lying close to the left posterior genital plate 
— or it may be the latter plate which has been abnormally divided. There is one 
pore in the madreporite and another in the right anterior genital plate. Genital 
pores are not yet developed. The peristome is as yet almost quite embryonal, the 
labrum scarcely beginning to project over it. The posterior end of the labrum lies 
off the end of the first adjoining ambulacral plate (PI. XI. Fig. 4). 
In a specimen of 1 1 mm. length the ambulacra have become somewhat petaloid 
in another specimen, 12.5 mm. long, they are more distinctly petaloid, as might be 
expected. In this specimen the labrum does not yet project over the mouth; its hind 
end is off the second ambulacral plate. Genital pores have not yet appeared. The 
globiferous pedicellariæ are very conspicuous, as seen in the figure (PI. XII. Fig. 1). 
Fig. 28. Abactinal plates of 
Amphipn. Koehleri , 7-5 mm. 
13.5/1. 
