TH. MORTENSEN, 



(Schwed. Siidpolar-Exp. 



and younger. The largest specimens from the marsupium correspond very nearly 

 to the stage of Abatus caveruosus 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. — Pedicellariae 

 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 Sa/enia, Ecliinus 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 mrn. 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 pedicellariae are very conspicuous, as seen in the figure (PI. XII. Fig. I). 



Fig. 28. Abactinal plates of 

 Amphipn. Koehleri, 7-5 mm. 

 13-s/i- 



