108 BULLETIN OF THE 
with the care and completeness I could have wished, I feel satisfied from 
the examination of several of the young, at a very early period, that in 
this case no provisional mouth, and no pseudembryonic appendages what- 
ever are formed, and that the primary aperture of the gastrula remains as 
the common mouth and excretory opening of the mature form.” Ina 
larva of an unknown Ophiuran, Krohn * finds the first infolding, “ Ver- 
tiefung,” in the position later occupied by the mouth of the adult. 
I am unable to quote any direct observations on the gastrula of Ophi- 
urans to show that the primary opening or gastrula mouth becomes a 
plutean anus. An anus is wanting in the adult Ophiuran. 
Although Apostolides criticises the explanation given by others of the 
method of formation of the openings into the internal cavity (stomach) 
of the gastrula by an invagination, he does not show how mouth or 
anus is in reality formed. As he does not show the old view to be erro- 
neous, and suggests nothing better, we must at present adhere to the 
commonly accepted explanation. The interpretation of Metschnikoff, 
who regards the first formed opening as a mouth, seems more reasonable 
than to suppose with Apostolides that itis an anus. Whatever it may 
eventually become, Metschnikoff’s suggestion, that it is formed by an 
invagination, conforms with what I have observed in the gastrula of 
Ophiopholis. 
In a short notice of the development of Ophiophragma, Professor 
Nachtrieb t refers to a blastopore, and a stomach “enteron” in its gas- 
trula. No infolding of the blastoderm to form this enteron is recorded, 
but the recognition of the primitive opening as a blastopore in another 
Ophiuran genus is worthy of notice.t I believe the gastrula stomach of 
Ophiophragma will be found to be formed by invagination as in Ophio- 
pholis. Professor Nachtrieb also studied the development of Ophiothrix, 
but his mention is too short to give me any information as to how he 
regards the gastrula stomach as formed. From what he does give it 
is supposed that the stomach is developed in the same way as that of 
Ophiopholis. 
Ophiocoma didelphys, Wyv. Th. See also general results of the voyage of the 
“Challenger,” by the same author, p. 241 et seq., Fig. 50. 
* Ueber einen neuen Entwickelungmodus der Ophiuren. Arch. f. Anat. Physiol. 
u. Wiss. Med. 1857. 
+ Johns Hopkins University Circular, March, 1885. 
¢ By a comparison of Apostolides’ figures of Ophiothrix it will be seen that the 
pluteus has pushed out the lateral arms to double the diameter of the body before 
a mouth or any external opening into the cavity of the pluteus is formed. 
