WYVILLE THOMSON, ON ASTERACANTHION VIOLACEUS. 103 



dilated at tlie free extremity into a slightly opaque^ rounded 

 tubercle, which at length takes the form of a sucker, undis- 

 tinguishahle from the ambulacral suckers of the young star-fish. 

 The dark granular fluid of the embryo still passes freely into 

 the tubular processes, through their wide, common base. 



This common base now contracts someAvhat, and lengthens, 

 and this narrower portion of the clavate embryo is separated 

 by a distinct line of demarcation from the broader mass, 

 which gradually assumes a still more rounded and definite 

 form. The whole embryo, during all these changes, increases 

 rapidly in size, partly by the imbibition of water through its 

 walls, and partly by the assimilation of organic matter 

 through its general surface. 



The dark upper part of the embryo is now rounded or 

 rudely pentagonal ; a thin, transparent, structureless layer, 

 with scattered oil-cells and bodies resembling endoplasts, 

 covers the whole surface ; a dark granular band lines the 

 transparent wall ; and the central space, lighter in colour and 

 more transparent, is filled with a mucilaginous liquid, turbid 

 with oil-globules, granules, and compound granular masses. 

 The lower end consists of a wide, transparent, contractile tube, 

 prolonged inferiorly into three, or sometimes four, wide 

 tubular branches ; and in the centre of the common peduncle, 

 between the branches, there is a whitish tubercle, resembling 

 in structure the substance of the suckers, and which 

 certaiidy has no central orifice. 



The peduncle and tubular appendages now assume their 

 definite and final form; all the specimens resembling one 

 another closely, except in the form of the thickest tube 

 foot, which is sometimes bifid at the point, that is to say, 

 provided with two suckers, and rarely bifid through nearly 

 its whole length. A slight constriction cuts ofi" the peduncle 

 into which these processes unite from the main embryonic 

 mass. The contents of the peduncle and tubes become more 

 and more transparent, till they consist merely of a clear, 

 colourless fluid, in Avhich chyle-corpuscles, of the usual form, 

 move and circulate, with the motion peculiar to such particles 

 in the vessels of the Echinoderms, and which Avould seem to 

 be produced by cilia, though the cilia themselves have not as 

 yet been detected. 



The embryo adheres to a foreign body by the suckers at 

 the end of the tubes, and moves along in a peculiar uncouth 

 manner, by the contraction and expansion of the three feet. 

 At this stage the peduncle is attached to the lower surface of 

 the pentagonal rudimentary star-fish, slightly excentrically 

 and midway between two of the projecting angles. The star- 



