211 Notes on the Embryology of Starfishes. 



We find beside?, in somewhat more advanced stages than 

 Figs. 1 and 2, in Fig. 3, at the anal extremity of the stomach 

 two independent bodies placed on each side of it (w' w", Figs. 3, 

 5, 10) resembling the water system of the young Brachiolaria in 

 a similar stage of development. These bodies are undoubtedly 

 part of the water system, as in more advanced stages they have 

 united (Figs, w' w", 6, 7, 9) and have increased in size towards 

 the oral extremity, and eventually unite with the large portion 

 of the water system {w) already formed at the oral extremity. 

 I have not followed this junction, although there seems but 

 little doubt that it does take place, as can be readily seen in 

 the good figure of a Tornaria given by Muller in his Sixth Me- 

 moir, Plate 9, which is somewhat older than any I have ob- 

 served,* to judge from the state of the water system. I have 

 frequently traced the junction of the separate bodies w' w" of 

 Figs. 3 and 10 till they had taken the shape of w' w", Figs. 7 

 and 9. It would follow from this that the anal part of the 

 water system of Tornaria is developed independently from the 

 oral portion, these separate parts eventually forming a junction ; 

 this is similar to the separate development of the right and left 

 branches of the Y-shaped water system in Brachiolaria. The 

 muscular band (in') which extends from the oral extremity (/) 

 of the Tornaria to the conical main cavity (w) of the water 

 system is quite powerful, and capable of changing the shape of 

 the main cavity of the water system by its sudden expansion or 

 contraction. 



We find in somewhat older larvae (Figs. 7, 8), as in Bra- 

 chiolaria, that the oral extremity increases more rapidly than 

 the anal, forming three abortive arms ; the edges of the groove 

 (g) in which the mouth (m) is placed, and which is bound by 

 the anal and oral vibratile chords, assumes a somewhat more 

 indented outline when seen in profile (Fig. 8) compared to ear- 

 lier stages (Fig. 3). These indentations never form arms pro- 



* See Muller's Sixth Memoir, p. 39 



