120 BULLETIN OF THE 
body where the umbilicus is joined to the edge of the disk (Fig. 12). 
Metschnikoff has figured them in the same position in Fig. 17 of his 
Plate IV. There seems abundant evidence that they are absorbed into the 
body of the forming Ophiuran, as in Ophiothrix and Ophiopholis. 
Ill. THE PENTAGONAL EMBRYO. 
There are two forms or conditions in which the pentagonal embryo is 
found. The one (Fig. 12) of these follows in age close upon the bilateral 
larva, and is still attached to the mother ; and the latter is represented 
by those larval stages when the young Amphiura has severed its connec- 
tion with the parent and is leading an independent life (Fig. 13). The 
exact time at which the umbilicus is broken was not observed, but the 
rupture takes place certainly a relatively long time before the young 
leaves the parent. The young larva then seems for some time to live free 
in the parent without umbilical connection. 
It becomes an interesting physiological question to determine the mode 
of alimentation of a young Amphiura in the body of the parent, and with 
no real connection with the adult. It would seem as if in older stages at 
least the young might be nourished by foreign matter taken into the open 
mouth. The genital slits of the parent would furnish an easy entrance 
for foreign bodies or small animals into the sacs, and the young Amphiuree 
while free in the body of the parents probably use these bodies as food. 
A.» THE » DISK. 
1]. PLaTEs OF THE ABACTINAL REGION OF THE DISK. 
Dorsocentral and Radials.—The aboral integument of the disk has 
embedded in it in young stages of growth six reticulated calcareous 
plates. These plates consist of a single central, dorsocentral (dc), and 
five radials, the primary radials or radialia (rp). These plates have been 
observed, figured, or described by Krohn,* Schultze,t Lyman,} A. Agas- 
* Op. cit., p. 341. Krohn figures (Pl. XIV. Fig. 1) a cross-shaped dorsocentral 
surrounded by a continuous calcareous ring with no separate radials. This ‘‘ einzigen 
Stiicke bestehende Kalknetz ” gives rise to ‘‘fiinf Schuppen.” The radials, accord- 
ing to a note on this page, are isolated from the beginning. 
+ Op. cit., p. 41. 
+ Ophiuride and Astrophytide, Old and New, Bull. Mus. Comp. Zoél., Vol. Ill, 
No. 10, p. 264. 
