SYNAPTA VIVIPARA. 73 



first appearance is bright green, even about the eyes, so that at this stage the eyes of 

 the young Synapta are very conspicuous as large green spots at the base of the tentacles. 

 Very soon, however, a dark reddish brown pigment appears, but this is probably an older 

 stage of the green, and not a different pigment; for the pigment around the eyes soon 

 loses its green color and turns brown, and there is no reason to assume that the pigment 

 in other parts of the body is any different from that around the eyes. All of the pigment 

 arises in the connective tissue, and is apparently a product of the mesenchyrne cells. It 

 is especially abundant at the anterior end of the body, and above all other places in and 

 around the calcareous ring. 



Before the number of tentacles is complete the ciliated funnels so characteristic of 

 Synapta begin to appear on the mesentery, near the body-wall. These funnels arise 

 from a large cell or group of cells in the endodermal epithelium of the mesentery (Figs. 

 61 and 62a). The multiplication of these cells soon forms a hemispherical outgrowth 

 (Fig. 62d) which increases in size and becomes more and more spherical in shape, until 

 it is finally attached to the mesentery by only a narrow stalk (Fig. 62e). It then begins 

 to flatten on one side, and the cells of its outer layers become smaller and stain more 

 heavily than those nearer the stalk (Fig. 62f). The flattened surface at last becomes 

 concave and the funnel shape begins to be assumed. At the same time, the stalk 

 becomes elongated and draws up within it some of the connective-tissue layer of the 

 mesentery, which becomes the supporting layer of the funnel. Even during the ten- 

 tentacled stage the digits of the tentacles begin to be formed, but they do not become 

 prominent until the twelve tentacles are all developed. The digits arise as evaginations 

 of the water-canal of the tentacle (Fig. 56) which very soon become shut off from the 

 main canal and in the adult have no connection with it (Fig. 55). The earliest ones to 

 appear are near the middle of the tentacle, and the later ones appear both proximally 

 and distally to them. The digits form longitudinal muscles on the outer side of the 

 central cavity in the same way as the tentacles themselves. They are also supplied with 

 nerves from the main tentacle nerve. The peculiar glandular organs of the larva are no 

 longer forming but seem rather to be disappearing, and the longitudinal rods of the 

 tentacles reach their maximum number at this time. The circumoral sinus, which was 

 entirely cut off from the rest of the coelom in the pentactula stage, has increased greatly 

 in size (Fig. 89) but is now in open communication with the body-cavity, though strands 

 of connective tissue traverse it, uniting the oesophagus to the water-ring and, higher up, 

 to the coelomic wall. With the greatly increased size of the young Synapta, comes a 

 considerable change in the relative position of the organs in the body-cavity. The body 

 has grown much posteriorly, drawing out with it that part of the intestine which lies in 



