242 Notes on the Embryology of Starfishes. 



2, 6, 7, 1 1'), and uniting on either side of the oral extremity 

 (Figs. 3, 8), where we have two very prominent chocolate- 

 colored pigment spots {/, Figs. 1, 2), the homologne of the bra- 

 chiolar pigment spots of Brachiolaria. The vibratile chords are 

 quite thin, and the loops would be barely perceptible as their 

 continuation were it not that the pigment cells, so generally dis- 

 tributed along their course in all Echinoderm larvae, retain an 

 unusual prominence (Fig. 4). These loops appear on the oral 

 surface of the Pluteus (Figs. 1, 2) like short oral arms project- 

 ing beyond the outline; as the Torn aria grows older (Figs. 6, 7) 

 the middle arm (/) becomes the most prominent. 



Besides the two vibratile chords (v, v') which can readily be 

 recognised as identical with the anal and oral chords of the 

 Brachiolaria, we have a vibratile chord (v" Figs. 1, 2, 3) of an 

 entirely different nature. It forms a complete circuit round the 

 body of the Pluteus (Fig. 5 v") and in the centre of it opens the 

 anus. It is covered like the others with brilliant pigment spots, 

 but the cilia forming the chord are large and powerful, and can 

 readily be distinguished as single threads without producing 

 the peculiar optical phenomenon of vibratile cilia, a common 

 feature in the embryos of Mollusks already observed by Muller. 



The Tornaria is quite transparent, and this is not diminished 

 in older larvae, as is the case in Brachiolaria, which when full 

 grown are quite opaque, so that the development of the Echi- 

 noderm could be very easily followed ; their motions are, how- 

 ever, much more rapid, and, as their name implies, they rotate so 

 constantly in every possible direction as to make it difficult to 

 observe them when not compressed. The digestive organs are 

 similar to those of Brachiolaria, though differing in their pro- 

 portions. The stomach (d, Figs. 3, 6, S, 9) is long and cylin- 

 drical, opening into a comparatively short intestine (e) which 

 trends in the same direction as the stomach, and opens at one 

 extremity of the Pluteus as in the very youngest stages of Bra- 

 chiolaria (a, Figs. 3, 6, 8, 9). The oesophagus (o, Figs. 3, 8, 9) 

 on the contrary is bent at a considerable angle and opens at the 



