112 BULLETIN OF THE 



and (2) The development of the pentagonal or stellate young, free in the 

 body uf the parent. 



The youngest embryo of Amphiura which was observed by me is a 

 blastosphere. 



Blasto&phere. — The blastosphere (Pi. 11. 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, anil is of about the same age as that of Amphiura figured 

 by Metschnikolf * and by Apostolides.f 



The few blastospheres of Amphiura which were ftnind were unat- 

 tached to the body walls or to each other. In later stages, as in the bi- 

 symmetrical larvae, the young Amphiura) are attached l)y 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 j\Iode of Propagation of certain Echino- 

 derms of the Southern Sea," X 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 blastosj)here are surrounded by two envelopes (??i^, m^). 

 I am unable to prove that either of these envelopes is " chitinartig," as 

 Metschnikolf describes the apparently homologous outer envelope. The 

 inner envelope resembles somewhat the cortical laj^er 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 arc spherical, red in 

 color. There is no ciliation on the outer surface of tlie 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- 

 tojilasm of the blastodermic cells two layers of cells, " von denen die 



* Op. cif.., PL in. Fig. 3. The "cavity" is lettered v (no explanation) in PI. III. 

 Fig. .5 ; cs in Fig. 4 (cs, Fig. 4, is the segmentation cavity), 

 t Op. cit., PL XII. Fig. 9. 

 } Jonrn. Lin v. Snc, XII. 

 § Op. cit., !>. 14. 



