bs BULLETIN OF THE 
not prevent our accepting the theory that the cavity of the gastrula is 
formed as Metschnikoff supposes. 
In Ophiopholis it has already elsewhere been shown that the archen- 
teron is formed by embole, and the known law of development in other 
Echinoderms would point to the same method in Amphiura. If there is 
an invagination of the blastoderm to form an archenteron in Amphiura, it 
is more masked than in Ophiopholis, and at present it is not possible for 
me to say whether Apostolides’ or Metschnikoff’s view of the mode of 
formation of the archénteron is the correct one. It looks very much as 
if the epiblast is separated from the reddish layer by a delamination, but 
it must be remembered that Amphiura is a viviparous genus, and possibly 
has a highly abbreviated * development in its early history. We may 
consequently suppose that more or less modification or concealment in the 
embolic mode in which the archenteron is generally formed in Echino- 
derms has resulted. It must also be remembered that the majority of 
gastrule of Echinoderms are embolic. My observations support in part 
Apostolides’ statement that the primitive cavity, not however the seg- 
mentation cavity, of the gastrula is the intestine (‘‘anus embryonnaire ”) 
of the future pluteus. Probably the stomach should have been included 
with the intestine. The external opening, if such exists, is early closed, 
and if it is lost, as it may be, from the attached life of the young Am- 
phiura, is probably always functionless. We have the following state- 
ment in regard to the anus of the young Amphiura. Apostolides states :f 
“Dans le stade suivant, ot l’ébauche du tube digestif est completement 
dessinée, on distingue bien au sommet de l’estomac, au milieu d’un bourre- 
let, Vorifice anal.” This would seem to show that there is an anal open- 
ing, but how it is formed cannot be answered so far as observation goes 
at present. 
In his first paper Metschnikoff recognizes an opening into the cavity 
of the larva, and considered it as formed by an infolding of the blasto- 
derm. He was probably mistaken in supposing this opening to be the 
primary opening, or blastopore. He is believed to have missed altogether 
* The “abbreviation in development which leads to the reduction in the arms of 
the pluteus stage in Amphiura is not believed to cause any great modification or va- 
riation in the development of the primary plates of the test and arms. One or two 
writers have brought to their aid, in speaking of the apparent discrepancy in the time 
of the development of these plates in Amphiura and an Ophiuran with a pluteus, the 
possibility of modification by abbreviation in the former genus. The argument is 
deceptive, and should not be given too great weight. 
+ Op. cit., p. 208. 
