494 W. WOODLAND. 



supporting a pocket-like protrusion of the dermal epitlielium, 

 it seems probable tbat the lateral extension of the knob to 

 form the recurved arms of the anchor-bow is, after all, but 

 an illustration of the deposition of skeletal matter in the 

 direction of least resistance. It is an elementary fact 

 that the anchor-bow does lie in a closely-enveloping derniiil 

 pocket, which is identical in genei-al outline with the bow, 

 and as fresh calcareous matter has for some reason to be 

 deposited at the knobbed extremity of the anchor-shaft, the 

 suggestion that the form which this additional deposit of 

 calcareous matter takes is largely determined by the envelop- 

 ing dermal pocket is not a very bold one. 



The objection that, were the form of this further deposit of 

 calcareous matter merely determined by mechanical pressure 

 this calcareous matter would simply assume a more or less 

 spatulate form and not the arms of an anchor, may be met 

 by the reply that the bow-form, which the calcareous matter 

 does assume, is not supposed to be solely due to the 

 mechanical contact of the dermal pocket. As is well known, 

 rod-structures in echinoderms generally have, for some 

 unknown reason, a tendency to bifurcate terminally, and 

 though the shaft of the Synapta anchor is abnormally large 

 owing to the large syncytium concerned in its production, yet 

 this is no reason why this rod should prove an exception to 

 the general rule. If this be the case, then the two arms of 

 the anchor-bow of Synapta must be regarded as the echino- 

 derm rod-bifurcations^ which in this case have been secon- 

 dai'ily reflected and otherwise modified by the special condi- 

 tions obtaining. Similarly, the handle of the anchor may be 

 regarded on this hypothesis as an abortive attempt of the 

 shaft to bifurcate at its internal extremity. 



It seems useless to attempt any further explanations in 

 connection Avith the form of the Synapta spicule, since such 

 explanations must necessarily, in our present state of know- 

 ledge, be vague and unsatisfactory. There is, of course, one 

 obvious question which every intelligent observer of these 

 spicules has asked himself, viz. why are the plates and 



