12 BULLETIN OF THE 
and (2) The development of the pentagonal or stellate young, free in the 
body of the parent. 
The youngest embryo of Amphiura which was observed by me is a 
blastosphere. 
Blastosphere. — The blastosphere (Pl. II. Fig. 1) was found free in the 
body of a dissected adult, and had probably ruptured its connection 
with the parent. It closely resembles the blastosphere of some other 
Echinoderms, and is of about the same age as that of Amphiura figured 
by Metschnikoff* and by Apostolides.f 
The few blastospheres of Amphiura which were found were unat- 
tached to the body walls or to each other. In later stages, as in the bi- 
symmetrical larve, the young Amphiure are attached by a structure 
called the umbilicus. Sir W. Thompson has spoken of the free young 
of certain viviparous Echinoderms in the body cavity of adults, in his 
“Notice of Peculiarities in the Mode of Propagation of certain Echino- 
derms of the Southern Sea,” { as not appearing to have in any case an 
organic connection with the parent. It seems natural to suppose, if 
the bisymmetrical larva is attached, that the younger stages are not 
free; but I have no proof of this. It is supposed, not proven by 
observation, that the blastosphere is broken from its attachment. 
The cells of the blastosphere are surrounded by two envelopes (m!?, m?). 
Iam unable to prove that either of these envelopes is “ chitinartig,” as 
Metschnikoff describes the apparently homologous outer envelope. The 
inner envelope resembles somewhat the cortical layer which I have de- 
scribed in the ovum of Ophiopholis where it is believed to be homologous 
to the zona radiata of other Echinoderms. Both envelopes are transpar- 
ent. Diameter, .13 mm. The blastodermic cells are spherical, red in 
color. There is no ciliation on the outer surface of the blastodermic 
cells. Nucleus of each cell well seen. There is a segmentation cavity 
(cav) as in other Echinoderms. 
Gastrula. —There is no free nomadic gastrula in Amphiura, but the 
blastosphere is followed by a larval condition (PI. II. Fig. 3), in which 
we recognize certain characters of a gastrula. According to Metschni- 
koff,§ directly after the blastosphere stage there appears in the pro- 
toplasm of the blastodermiec cells two layers of cells, “von denen die 
* Op. cit., Pl. III. Fig. 3. The ‘‘cavity” is lettered v (no explanation) in P1. III, 
Fig. 5; cs in Fig. 4 (cs, Fig. 4, is the segmentation cavity). 
+ Op. cit. Pl. XI, Fig! 9: 
t Journ. Linn. Soe., XII. 
§ Op. cit., p. 14. 
ee 
