16 BULLETIN OF THE 



nals seem to arise almost simultaneously, although brachiolarise have 

 been found with two, three, or four terminals. The five terminals are, 

 however, all believed to be formed before the genitals appear. The ring 

 of terminals, beginning with t^ near the madreporic body, are placed 

 in their U-shaped figure at about equal distances apart, with the excep- 

 tion of t^ and t^. The space between these two last is the whole diam- 

 eter of the stomach of the brachiolaria. This space, which in older 

 stages appears as a notch separating the fii'st genital, g^, from the fifth 

 terminal, t^, is the brachiolarian notch. It is the notch which marks 

 the position of the madreporic body, and renders it a point of departure 

 in all morphological comparisons of the different groups of Echinoderms. 

 The notch and madreporic opening are separated by the first genital, g\ 



The stage of the young starfish directly following the one in which 

 the dorsocentral is first seen shows a condition in which the terminals 

 have elongated and extended Y-shaped appendages at their extremities. 

 These extensions have formed a rod perpendicular to the radius connect- 

 ing the dorsocentral with the margin of the formiug starfish. The law 

 of the first growth of the terminal seems to be that they elongate, form- 

 ing an extension across perpendicular to the radial lines, not parallel with 

 them. The spines of the terminals appear directly after the dorsocentral, 

 while yet the terminals are simple spicular bodies. Notches now begin 

 to deepen in the interradii of the forming starfish on the border of the 

 disk, separating the terminals. The terminals never coalesce with their 

 neighbors. Although the terminals originate in the body of the starfish 

 while yet a swimming brachiolaria, and form the most conspicuous 

 plates in the Asterias before the stellate form is marked out, they are 

 ultimately pushed to the extremities of the rays by the growth of the 

 plates of the arms. The first appearance of the stellate form of the 

 young Asterias results from the enlargement of these plates. The ter- 

 minals originate on the abactinal side of the body, and grow down on 

 the sides of the water-vascular portion of the extensions from this sys- 

 tem. By this growth they eiiclose the tube above and on two sides, 

 and come to have a cap-shape, an opening being left on the terminal 

 border for the passage of the tentacle. There is no growth downward 

 at the tip of the radii in which they lie, but a groove is left at that 

 point through which later the extremity of the medial vessel extends, 

 and in which point the eye-spot is situated. 



The cap-shaped form of the terminals affords ample protection for the 

 immature ambulacrals, am, intei'ambulaci'als, ad, and marginals, m, 

 which first form under cover of the sides and dorsal portions of the 



