EESOEPTIOX OF THE BRACHIOLAEIA. 41 



Bi-achiolaria (PI. VII. Fig. 8) lias almost entirely disappeared, and the 

 embryo Starfit^h has taken its place (PL V. Figs. 9-14). This embryo 

 is so heavy that, when floating about, it loads down the anal part, which 

 is always the lowest, and the larva is compelled to move always more 

 or less obliquely, having to drag this great weight after it. The water- 

 pore remains in the position in which it w^as at first, in the angle of the 

 arm {i\), which opens the pentagon, and is encased in a stronger deposit 

 of limestone. 



Resorption of the BraduoUria. — While the Starfish is growing upon the 

 outer surfaces of the two opposite water-tubes, and is gradually becoming 

 a part of the Brachiolaria, no changes take place in the external appear- 

 ance of the larvjB (PI. IV. Figs. 1, 2 ; PI. VII. Fig. 8). But when the 

 Starfish has become so far advanced as to occupy a very prominent posi- 

 tion at the anal extremity of the larva (PI. IV. Fig. 4; PI. VII. Fig. 8), 

 the complicated appendages designated as arms, which have served for the 

 development and for the locomotion of the Starfish, are resorbed by the 

 little Echinoderm. 



"We now come to a most interesting period in the history of our Star- 

 fish. The larvne, very active up to this time, grow sluggish ; the body, 

 which, with the exception of the anal portion, is, in the early stages, 

 perfectly transparent and clear, becomes cloudy and opaque. Changes 

 are first visible in the side arms (PI. IV. Figs. 7, 8, 9); thej' contract, 

 and apparently divide into many large cells. Next in turn the anal ven- 

 tral arms, and, lastly, the dorsal arms, contract in the same manner. This 

 contraction of the arms is accompanied by a corresponding shrinking of 

 the anal part of the larva, beyond the mouth (PI. IV. Fig. 9j, so rapid 

 that in a few hours the anal arms have shrunk to quite a small compass 

 (PL IV. Fig. 9); the oral dorsal arms and the oral ventral arms contract 

 in their turn, until there remains nothing but the brachiolar arms, brought 

 close to the Starfish by the shrinking of the mass of the body (PL IV. 

 Fig. 8). They soon follow the rest, and we can actually see the gradual 

 disappearance of this complicated fabric. It has served its purpose of 

 developing and feeding the young Starfish, which has now reached a state 

 when, in a few hours, it will move about independently, having resorbed, 

 for what purpose is not known, the whole of the framework. Not a single 

 part is dropped off, the wliole of the larva passes into the Starfish, and, before 

 twelve hours have elapsed from the commencement of the first sign of 



