SPICULES OF SYNAPTA AND AURIOULARIA LARVA. 487 



next elongates on one side (figs. 3 and 4) in a direction 

 transverse to the long axis of the animal. Thus, remarkable 

 as it may seem, the minute rod which the granule gives rise 

 to, and which, in its turn, becomes the anchor of the adult 

 spicule, is from the very first orientated in the direction 

 assumed by the full-grown structure. The process formed 

 from the side of the initial granule (situated to the right or to 

 the left of the observer, as the case maybe) continues to grow 

 (figs. 5-10) until there is produced a stick-like structure, 

 equal in length to the future anchor. One end of this stick- 

 spicule is somewhat swollen to form a knob, and represents 

 the unmodified half of the original granule — the other half 

 having grown out to form the stick. The stick is also usually 

 of slightly greater diameter mid-way in its length than 

 towards its extremities ; in other words, the stick tapers 

 somewhat, both towards the knobbed and the pointed ends. 

 Also it possesses, at this stage, a distinct axial thread. The 

 nuclei of the syncytium, up to this period of growth, and until 

 the knobbed end of the stick has produced the recurved arms 

 of about half the adult length, remain, for the most part, on 

 the outer side of the stick — i. e . towards the external dermal 

 layer — although one or two may be situated more internally 

 (figs. 9, 10, 11). I may also mention that the syncytium 

 surrounding the spicule usually remains in connection with 

 the epithelium from which it originated by means of a few 

 irregular protoplasmic strands. 



The next stage in the development of the anchor spicule is 

 the protrusion of both sides of the knobbed extremity of the 

 stick or shaft to form the arms of the future bow of the anchor 

 (fig. 10). These incipient arms elongate, and very soon 

 become recurved ; at the same time this lateral extension of 

 the knobbed extremity stretches the substance of the syn- 

 cytium enveloping the spicule so as to produce the appearance 

 shown in figs. 16 and 18. 



When the arms of the anchor have become half-grown a 

 very remarkable phenomenon occurs in connection with the 

 syncytial nuclei, situated a little bow-ward of the middle of 



