26 EMBRYOLOGY OF THE STARFISH. Part I. 



almost be tempted to believe they join, like the oral portions, and thus form a 

 complete circuit (PL III. Fig. 10) ; this, however, is not the case, as an examination 

 in profile of the above figures readily shows. 



First Appearance of the Starfish. — In the drawings here given to illustrate the 

 development of the Starfish, only a small portion of the Brachiolaria is figured, that 

 which has direct reference to the Starfish itself; as this part is limited to the anal 

 extremity of the larva immediately surrounding the stomach, the anal extremity 

 alone of the Brachiolaria is drawn, with the arms ciit off, somewhat beyond the open- 

 ing of the anus. To make the references to the figures of Plate V. more satisfactory, 

 a reference has also been made to a drawing of a whole Brachiolaria, in a stage of 

 growth nearly identical, in order to show more readily the relation of the Starfish to 

 the whole framework of the Brachiolaria. These stages are so similar that, with 

 this explanation, it will always be possible to refer the anal extremities, upon which 

 we are tracing the development of the Starfish, in its different phases of growth, to 

 some figure of Brachiolaria, very nearly representing its actual condition. The 

 stages of development figured in Plate V. have been selected without reference to 

 the Brachiolaria, and simply for the sake of the young Starfish, and would, if drawn 

 on the same scale as the other figures of the Brachiolaria here given, show no 

 differences, which would make the mode of growth of the young Echinoderm more 

 intelligible. For instance, the earlier stages of the development, such as Figs. 1-7, 

 correspond to the stage of PI. III. Fig. 10 ; while the more advanced Fig. 8, corre- 

 sponds to that of PL III. Fig. 11, and the others to the adult stages of the Brachiolaria 

 on Plate IV., when the Starfish undergoes extensive changes, while none take place 

 in the general appearance of the Brachiolaria. 



Up to the stage of the larva represented on PL III. Fig. 6, 7, the outline of the 

 left water-tube {left when seen from above in its natural attitude), in a profile view, is 

 that of a flattened cylinder (PL V. Fig. 1, w), with the end slightly bent towards 

 the anal opening. There is formed, near the point where the upper line of the 

 water-tube bends downwards, a marked indentation, having in the centre a slight 

 projection. There appear, soon after starting from the anal edge of this depression, 

 five very faintly-defined folds, the first trace of the future ambulacral system, extend- 

 ing obliquely across the water-tube (w') (PL V. Fig. 2, t; PL III. Fig. 8). If we 

 examine the other side of the anal extremity, we find deposited, opposite the angles 

 of these folds (PL V. Fig. 2, /'}, five rods of limestone ; the anal part of the larva 

 having at the same time lost its former transparency, and assumed a dull-yellow color. 

 These two parts are the first traces of the future Starfish. The limestone rods, and 

 the whole of the granular surface covering the right water-tube, with the dorsal pore, 

 forms eventually the abactinal area of the adult Starfish. While the folds, running 

 obliquely across the left water-tube, are the first rudiments of what is to become the 



