118 BULLETIN OF THE 



rical larva it is present, but has been ruptured in the young larvae which 

 he has figured prior to that represented in Fig. 1 7, and will be seen figured 

 in my plate in some of these or corresponding stages. 



Of the ultimate fate of the " Nabelschnur " (u) Metschnikoff says:* 

 "Daer iiber schliesslich (ebenso wie das provisoriche Kalkskelet) ver- 

 schwindert, ohne in den Kdrper des sich bildenden Sternes direct Uberzu- 

 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" partf of the larva figured in 

 Fig. 7 passes by absorption into the embryo. 



As to what part of the bisyrametrical larva is the homologue of the 

 pluteus of Ophiopholis it may be said that the Amphiura 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 (Hydrocoelen) 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 tlie right vesicle 

 until we know the origin of the right " Scheibe," or enterocoel. 



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. ciL, p. 18. 



t The protuberance on the right-hand upper corner of the figure imparts to the 

 larva a hunchbacked appearance. All of this protuberauQe is absorbed in the growth 

 of the young Amphiura, 



J Op. cit., p. 16. 



