Kirk. — Much-abbreviated Development of a Sand-star. 383 



Art. XXXVI . — On the Much-abbreviated Development of a Sand-star 

 (Ophionereis schayeri?). — Preliminary Note. 



By H. B. Kirk, M.A., Professor of Biology, Victoria College, Wellington. 



{Read before the Wellington Philosophical Society, 27th October, 1915.] 



Plates XXVn, XXVIH. 



I OBSERVED at Island Bay in August of this year several clusters of small 

 round eggs attached to the underside of stones. Some of these were brought 

 in on the 24th August, and observed from time to time to determine, if 

 possible, to what animal they belonged. Only slight attention was paid 

 to them, but they were probably not left unobserved for more than two 

 days together. To my great surprise, there began to emerge from the eggs 

 of one group small Echinoderms having the general appearance of Asteroids 

 with a perfectly formed disc that had the barest suggestion of arms. Each 

 had the primary tube-feet developed beyond the extremity of the radial 

 groove. The tube-feet had somewliat club-shaped extremities, withoiTt 

 suckers, but with a number of stifi, bristle-like processes. Each of the 

 five points of the disc consisted of a single, grooved terminal plate like that 

 of Ophionereis schayeri Miiller and Troschel. There could be no doubt that 

 the young animals were Ophiuroids. 0. schayeri is very common in the 

 neighbourhood. I have often examined the bursae, and have never found 

 them to contain embryos. 



I carefully observed the remaining capsules, and obtained others from 

 the same locality ; but the time for the very early stages had gone by. 

 From these later observations, and from the earlier but less thorough obser- 

 vations, I am able to give the following preliminary account of this very 

 extraordinary instance of Echinoderm development. 



The eggs are spherical, 0-5 mm. in diameter, each with a perfectly trans- 

 parent, thin, but extremely tough chitinous envelope. They are deposited 

 in irregular clusters of from 10 to 100 or more. The embryo does not 

 occupy the whole of the space within the envelope, but is surrounded by 

 colourless, apparently mucilaginous, matterr The envelope was so tough 

 that I could not tear it away satisfactorily, the embryo getting crushed in 

 the process. The embryo is of a buff or pinkish-brown colour, and is so 

 opaque that no internal structure is to be observed. The pigment is very 

 refractory to all the ordinary solvents. For knowledge of internal structure 

 sectioning is likely to be the only process, and for this I shall have to obtain 

 fresh material next year. 



The earliest embryos observed were apparently late gastrulae, in which 

 the blastopore had closed or become indistinguishable. No movement was 

 at any time observed until the disc and tube-feet were formed. I do not 

 think that any external cilia were ever developed, or that there was any 

 stage that could be recognized as corresponding at all closely to a typical 

 larval stage of any Echinoderm. My present view is that development is 

 absolutely direct, but I cannot yet speak with certainty. 



The first movement observed was that of the tube-feet. At the time 

 these appear the disc is concave on the ventral sixrface, the tube-feet 



