Pedicellarice in the Echinidae. 105 



this and the stem of one of the pedicellariaai upon which no 

 such dilatation is known to occur. It will be found, however, 

 on examination under the microscope, that the foramina are 

 nevertheless present and occupy the same position as that 

 which they would hold in one of the sac-bearing' stems, and 

 appear to be normal in every way (PI. XII. fig. 6). I am 

 led, therefore, to regard these as simply cases in which the 

 glands of the sacculi are aborted from some cause or other ; 

 but how this state of things has come about I am quite 

 unable to say. 



Head of the Pedicellaria globifera. — Mucus, as previously 

 stated, is extruded from the head or jaw-portion of the ped. 

 glohifera. As the anatomy of the soft parts of these organs 

 has never been described in detail, it will be found a subject 

 well worthy of attention on the present occasion, and will 

 assist in the elucidation of the functions performed by these 

 well-known and yet obscure appendages. 



The structure of the calcareous framework of the head of 

 this form of pedicellaria is familiar to most possessors of 

 microscopes, and has been frequently figured. It is at once 

 readily recognizable from that belonging to the triphylla or 

 tridens form of pedicellaria. Each of the three valves or 

 jaw-pieces of the ped. globifera in question is of remarkably 

 elegant form, somewhat resembling a mandolin in shape. 

 The basal portion is large and swollen out, presenting a 

 convex surface outwardly and a concave one inwardly, a 

 delicate median keel or partition separating this latter into 

 two hollow chambers. The basal portion occupies fully one 

 third of the height of the jaw-piece. The upper portion 

 consists of a delicate shaft proceeding from the upper part 

 of the basal shield in the prolongation of its median axis • 

 it is somewhat quadrangular in section, and slightly tapers 

 towards the upper portion ; the extremity is finely pointed 

 into a tooth-like process, which is roundly curved at a right 

 angle to the axis of the piece and directed inwards ; imme- 

 diately where the curve is completed the shaft becomes 

 somewhat constricted, and is then slightly expanded again 

 prior to the commencement of the delicate tapering towards 

 the tip, the expanded portion being channelled and presenting 

 the appearance of two or more lateral lamella? merged toge- 

 ther to form the tip or tooth-like fang. The valves of the 

 pedicellaria globifera are attached immediately to the upper 

 part of the calcareous shaft of the stem. The whole head is 

 invested with a very considerable development of soft parts, 

 and presents, when closed, the appearance, so aptly described 



