ON THE EMBRYOLOGY OF ECHINODERMS. 



27 



EXPLANATION OF THE FIGURES. 



WiTn the exception of fjgs. 29, 30, and 34, which were copied from drawings made bv Mr. Tappan, under 

 the direction of Professor Agassiz, the figures were drawn on wood by myself from tlie drawing-; I made at 

 the time of this investigation. 



TOXOPNEUSTES DROBACHIENSIS Ao. 



Figs. 1-28. 



The specimens from figs. 1-18 inclusive were all obtained from artificial fecundation; figs. 19-27 were 

 caught with the dip-net ; fig. 28 was thrown up on the beach after a storm. 



EXPLANATION OF LETTERING. 



a, anus. 



b, madreporie body. 



c, alimentary canal (intestine). 



d, digestive cavity (stomach). 



e', e", e'", e", arms of the plutean form. 



f, brachiolar arms ? 



g, tentacles round actinostome in Cuvieria. 

 g', ambulacral tentacles of Cuvieria. 



k, teeth of young Echinus. 



/, body of larva of Cuvieria (pupa of Miiller). 



m, mouth. 



n, interambulacral tubercles of Echinus. 



n', ambulacral tubercles. 



0, oesophagus. 



p, pedicellaria. 



r, abactinal region. 



r', main rod, formed first in the Echinus Pluteus. 



r", rod of arm e". 



r'", independent rod above oesophagus. 



r", anal point of junction of rods in the Ophiuran Pluteus. 



s, actinal region. 



s', spots of arms e', e" of the Pluteus of Echinus. 



s", interambulacral spines of Echinus. 



s'", younger spines of Echinus. 



t, tentacles. 



t', odd terminal tentacle. 



V, anal part of vibratile chord. 



v', oral portion of vibratile chord. 



v", vibratile epaulettes. 



■w, water-tube. 



w', water-tube leading to madreporie body. 



y, terminal arm-plate of Oj)liiuran. 



y', side arm-plates of Ophiuran. 



In fig. 31 t> should be v', and vice versa. 



For the earlier stages compare figs. 1 - 5 of Proc. Am. Acad., from which the earlier stages of the Echinus 

 Pluteus do not differ greatly. 



Fig. 1. Profile view of an Echinus Pluteus eighty-eight hours after artificial fecundation. 



Fig. 2. The same as fig. 1, seen from above. 



Fig. 3. Profile view of a plutean form somewhat more advanced than in fig. 1 ; the digestive cavity, d, is 

 bent very considerably towards the actinal side. 



Fig. 4. View from above of a Pluteus in which the digestive cavity, d, is somewhat differentiated by con- 



