118 BULLETIN OF THE 
rical larva it is present, but has been ruptured in the young larve which 
he has figured prior to that represented in Fig. 17, and will be seen figured 
in my plate in some of these or corresponding stages. 
Of the ultimate fate of the ‘“ Nabelschnur” (w) Metschnikoff says : * 
“Da er tiber schliesslich (ebenso wie das provisoriche Kalkskelet) ver- 
schwindert, ohne in den Korper des sich bildenden Sternes direct iiberzu- 
gehen, so muss man seine Riickbildung durch Atropie annehmen.” That 
a part of the umbilicus and the whole of the provisional skeleton of the 
pluteus is absorbed seems to me true, as traces of the provisional skeleton 
(ps) are found in the pentagonal larva even when free from the mother. 
Of the freedom of the oldest stage when the remnant of the plutean skel- 
eton was observed there may be doubt; but there can be little question 
that this skeleton enters into the formation of the future starfish, al- 
though possibly not directly into the formation of any special organ. 
It is thought that all the “hunchback” part t of the larva figured in 
Fig. 7 passes by absorption into the embryo. é 
As to what part of the bisymmetrical larva is the homologue of the 
pluteus of Ophiopholis it may be said that the Amphinra young is a 
pluteus without arms, although the calcareous framework of the lateral 
arms is present. The larva (Fig. 7) is a pluteus with aborted arms. 
Water-tubes and “ Lateral Scheiben.” — In the early stages of growth 
up to the pentagonal larva the water-tubes (Hydroccelen) and the lateral 
bodies (Enteroccelen) were seen, but nothing new added to our knowledge 
of these structures. In one larva the right-hand water-tube is present 
after the left has begun to push out the five extensions which form the 
terminal tentacles. This tube was thought to open externally, and near 
its opening a trifid calcification was observed. It is known that mon- 
strosities so called in the development of the tubes are said sometimes to 
give us a larva with even a pentamerous right water-tube, and it may be 
that this development belongs in this category. It does not seem reason- 
able that the right-water vesicle disappears, as stated by Metschnikoff. $ 
We must wait in answer to the question of the fate of the right vesicle 
until we know the origin of the right “ Scheibe,” or enteroccel. 
Observations upon the origin of the water-tubes of the Ophiurans are 
very much needed in the present state of science, and we can hardly put 
* Op. cit., p. 18. 
t The protuberance on the right-hand upper corner of the figure imparts to the 
larva a hunchbacked appearance, All of this protuberance is absorbed in the growth 
of the young Amphiura. . 
+f (Op: cit... p. 16: 
