26 EMBRYOLOGY OF THE STARFISH. 



tapering to a point in the odd brachiolar arm, enclosing the stomach and 

 oesophagus, which form, as it were, a soUd axis to this elliptical envelope. 

 On one side of the stomach appears a large hole (PI. V. Fi(). 7, h, anal 

 part only; PL VII. Fig. 8), the opening of a cul de sac of one branch of 

 the water-system passing between the stomach and the intestine. The 

 portions of the water-system extending along the stomach appear to be 

 made up of distinct chambers (PI. V. Figs. 6, 7, 8, w, vl) : these cham- 

 bers are merely the result of an optical delusion, arising from the greater 

 or less flattening of certain parts of the tube ; this gives it the appear- 

 ance of having been divided off into segments. 



The Adult Larva. — The anal part of the larva, in its adult condition 

 (PI. IV. FigH. 1, 2), has become pointed ; the general shape is still some- 

 what rectangular; the ventral and dorsal side are separated by a deep 

 groove (PI. IV. Fig. 4), extending from the stomach, from the base of 

 the median anal pair of arms, to the base of the ventral oral arms, thus 

 separating the larva into very distinct dorsal and ventral regions (PI. IV. 

 Fig. 4), from the earliest stages of its growth. The body of the larva 

 itself is capable of great motion ; nothing is more common than to see 

 the larvae almost broken in two, by the strange habit they have of bend- 

 ing the oral extremity upon the opening of the mouth as a pivot, to such 

 an extent as to make quite an angle with the anal part (PI. III. Fig. 5). 

 The larvae generally assume this position when disturbed, and usually 

 remain stationary in the same attitude, simply striking violently up and 

 down with their extremities (compare Fig. 5 and Fig. 2, where the larva 

 is at rest). The whole substance of the body is tinged with yellow, and 

 is made up of large transparent cells with irregular nuclei, giving the 

 mass about the consistency of a Salpa; very minute granular epithelial 

 cells cover the whole surfoce. The powerful contraction of portions of 

 the body is simply that of the cells themselves, and what has frequently 

 been mistaken by Miiller, when describing these larvre, for muscular stria?, 

 are strings of such contracted cells. The extremities of the arms are 

 tipped with orange, the stomach and the alimentary canal are of a slight 

 yellowish-brown color, the chords of vibratile cilia are somewhat darker. 

 The oesophagus is perfectly transparent, capable of violent movements; 

 it expands and contracts by sudden jerks, forcing open violently the 

 passage leading into the stomach, when the contents of the oesophagus 

 rush in, and are set slowly rotating in the stomach. The interior surface 



