M. Sars on the Development of Star-fishes. 235 



in form. This then is the first or Infusorial stage of structure in 

 the Star-fish. After a few days, organs (fig. 12, a a) begin to 

 grow from that extremity of the body which during swimming was 

 directed forwards. These, which are to serve the purposes of attach- 

 ment, appear in the shape of papillae ; first of all one on one side 

 (fig. 12), then two smaller ones upon the other (fig. 13, 13 b, aa) : 

 subsequently the first divides itself into two, so that we now meet 

 with four such papillae of nearly equal size and club-shaped 

 (figs. 14 — 16, a a), and in the middle between them a smaller one 

 (figs. 14 — 16, b). By aid of these organs the young fixes itself 

 firmly to the walls of the uterine cavity. The body now becomes 

 flattened, depressed (figs. 14 — 17) and circular, and upon one of 

 the broad surfaces, which is thus proved to be the ventral, the 

 tentacula begin to sprout forth as small round papillae, radiating 

 in ten rows from a common centre ; two of which are approxi- 

 mated together, there being only two papillae in each row 

 (fig. 14, c c). Upon being detached from the spot to which it had 

 fixed itself, the young still swims in the water through the agency 

 of its vibratile cilia, and always with the organs of attachment 

 directed forwards ; but when undisturbed it adheres firmly and 

 immoveably to the place of attachment, never once quitting it. 

 In this condition, or the second stage of development, which has 

 been called the Crinoidal, — for we know of no other class of Star- 

 fishes, except that of the Crinoidea, which are sessile, at least when 

 young, to compare it with, — the young Asterias is still bilateral in 

 symmetry, and the organs of attachment are seen to be constantly 

 directed forwards, and by means of the organs (figs. 14, 15, a a) 

 already mentioned as being unequally developed upon the two 

 sides of the body, an anterior and posterior, as well as a right and 

 left side, may be defined. The dorsal and ventral surfaces are 

 already indicated by the tentacula. By degrees, however, this 

 bilateral form passes into the radiary, the third and perfect stage 

 of development in the Star-fish, in which the body becomes pen- 

 tangular by its border growing out into five very short and ob- 

 tuse arms (figs. 18, 19). The tentacula lengthen out into cylin- 

 drical tubes (fig. 20, c c) with sucking-cups at their extremity, to 

 assist them in the act of creeping. At the apex of the arms we 

 remark the organ regarded by Ehrenberg as the eye (fig. 18, b) ; 

 the mouth presents itself to view upon the ventral surface, and 

 numerous spines (figs. 1 9, 20) grow upon the integument of the 

 body and arms. By and by the organs of attachment begin to 

 diminish gradually in bulk (fig. 20, a a) and finally to disappear, 

 the swimming movements to cease with the obliteration of the cilia, 

 and the young Star-fish, now become completely radiated in form 

 (fig. 20, a a), creeps freely about by means of its still dispro- 

 portionately long tentacles (fig. 21, c c). The whole of this de- 



