106 BULLETIN OF THE 
These are the most important references which have been found to the 
embryology of this, one of our most common Ophiurans. My observa- 
tions differ radically from the statements quoted. 
The eggs of Ophiopholis are cast free in the water, and the young pass 
through a metamorphosis, in which a larva commonly called the pluteus 
is formed. The mode of development of this pluteus is different from 
that of any Ophiuran which has yet been described. It is most closely 
allied to that of Ophiothrix, but in the mode of formation of a gastrula 
differs widely from the account of a species of Ophiothrix, “ 0. versicolor,” 
traced by Apostolides.* 
The formation of the gastrula in Ophiurans has been very unsatisfac- 
torily studied. An invaginated gastrula has never been figured in this 
group. Balfour f in a short notice states that he has observed in Ophio- 
trix that the gastrula stomach is formed as in other Echinoderms by an 
invagination (of the blastoderm). The same mode had previously been 
suggested as probable by many embryologists, and had found its way 
into all the more important text books. It is not accepted by Aposto- 
lides, one of the latest students of the development of these animals. 
Apostolides { strongly combats the explanation of the method of for- 
mation of the gastrula by invagination, and brings forward new observa- 
tions on Ophiothrix, the same genus studied by Balfour, to show that 
no invagination of the blastoderm occurs, and that the hypoblast of the 
stomach is formed from cells in the inside of the blastosphere. To these 
observations he brings as aids his studies of Amphiura to prove that in 
Ophiurans the normal method of invaginated gastrule does not exist. 
The observations, therefore, which I have made, are thought to have a 
morphological importance as supporting the a priorz views of most em- 
bryologists, and the direct observations of Balfour on another genus, of 
the method of formation of the stomach of the pluteus of Ophiurans by a 
primitive invagination of the blastoderm. I have never observed the gas- 
trula of Ophiothrix, and can speak with confidence of Ophiopholis only, 
as far as this point is concerned. The differences between Apostolides’ 
* Je These. Anatomie et Développement des Ophiures. Arch. d. Zool. Exp. et 
Gen. X. Apostolides does not seem to have sufficiently studied tlie descriptions of 
the various species of Ophiothrix in the writings of Ljungman (Oph. Of Kong. Akad. 
p. 625, 1871. Description of O. Lusitanica), and Lyman (Bull. Mus. Comp. Zoil., 
Vol. III. Part 10, pp. 240-249). The “‘ O. versicolor,” Apostolides, is probably, as 
has been suggested to me by Mr. Lyman, the same as O. Lusitanica, Ljn. 
+ A Treatise on Comparative Zoology. 
t Op. cit., pp- 192 and 207. 
