242 



PROFESSOR ALLMAN ON A PRE-BRACHIAL STAGE 



retracted, the triangular plates become approximated to one another at their 

 edges, and then each will form the side of a pentangular pyramid. The height of 

 this pyramid is about equal to the depth of the cup, so that the entire body has 

 then somewhat the appearance of two nearly equal pyramids placed base to base ; 

 but when the animal is about to expand, the sides of the roof separate from one 

 another, and opening outwards like the segments of a calyx in an expanding 

 flower-bud, allow the flexile appendages already mentioned to come into view ; 

 and these, gradually elongating themselves, finally fall down gracefully over the 

 edge of the calyx (fig. 1). 



Both the calyx and roof are solidified by the deposit in them of mineral 

 matter. The deposition, however, takes place in such a way as to leave a mul- 

 titude of minute spaces free from it, so that the whole presents a kind of reticu- 

 lated structure, which, while it is a characteristic echinodermal feature, adds 

 much to the elegance of the little Crinoid. The membranous basis in which the 

 earthy matter is deposited extends a little beyond the margin of the valve-like 

 plates of the roof, and by transmitted light may be seen forming also a narrow 

 transparent contour round the entire body. 



Long flexile appendages, or cirri, have already been mentioned as rising out 

 of the calyx. These, in the expanded state of the animal, are thrown out between 

 the edges of the five diverging plates of the roof, and thence hanging down all 

 round over the calyx, afford an additional element in the beauty of our little 

 Crinoid. I have counted fourteen of these cirri, but they may be more numerous, 

 for it is very difficult to determine their exact number. They appear to be cylin- 

 drical, with a canal occupying their axis ; and as far as they can be traced back- 

 wards, they are seen to be furnished with two opposite rows of rigid setse or fine 

 blunt spines (fig. 4). Between every two opposite setse a transverse line may be 

 seen stretching across the cirrus, and indicating its division into tranverse seg- 

 ments. Of the base of the cirri I can say nothing. I have never succeeded in 

 getting a view sufficiently deep into the space included within the five roof- 

 plates, to allow of my tracing those appendages to their origin. 



Besides the long extensile cirri now described, there is also an inner circle 

 of short, apparently non-extensile, appendages. It was only occasionally that 

 I succeeded in getting a glimpse of these; they appear to constitute a circle 

 of slightly curved rods or narrow plates, proba.bly five in number, which arch 

 over the centre, and are provided along their length with two opposite rows of 

 little tooth-like spines ; they seem to be articulated to the upper or ventral side 

 of the calyx by their base, and may be seen in a constant motion, which consists 

 in a sudden inclination upon their base towards the centre, followed immediately 

 by a resumption of their more erect attitude. 



Our little Echinoderm is very irritable, and on the slightest annoyance the 

 cirri are suddenly withdrawn, and the valve-like plates of the pyramidal roof 



