106 Mr. W. Percy Sladen on the 



by Valentin, of the corolla of a flower " asleep " for the 

 night *. 



Each jaw-piece is invested in a membranous sac, which 

 gradually swells out from the tip to the base, where it pre- 

 sents a very inflated appearance, and merges into the general 

 sac of the whole head, the only portion of the calcareous 

 shaft that is visible being the fang or tooth-like process, 

 which is left naked and protruding from the apical portion of 

 the sac. On the upper surface of the fang the investing 

 membrane does not lie perfectly close to the shaft ; but an 

 aperture is formed on either side, through which mucus is 

 expelled. 



No trace of the two external sac-like formations that are 

 found in the pedicellarim globifercc of many other Echini is 

 visible to superficial view in those of Sphcerechinus granu- 

 lans, the whole valve being enveloped in a single, highly 

 inflated, membranous sac. 



The valves of the pedicellaria can be opened and closed, 

 the expansion being generally maintained until the inner 

 surface of the valves is at right angles to the shaft, and the 

 inner areas of the three jaws together form a plane flat 

 surface at right angles to the stem. When in this position 

 the fang is usually retracted, or, perhaps more correctly, hidden 

 within the sac-like sheath (PI. XII. figs. 3-5). At the 

 slightest touch or irritation the jaws immediately close, and, 

 under certain circumstances, a flow of mucus takes place from 

 the apertures above mentioned. 



Recourse must now be had to dissection and sections in 

 various directions, to enable us to treat further on the anatomy 

 of the organs under consideration. 



On examining a longitudinal section through the pedicel- 

 laria the following tissues will be observed: — 1. The fine 

 investing membrane composed of epithelial cells ; 2. A stra- 

 tum with a few distributed nerve-cells ; 3. The walls of a 

 large saccular body bounded by a moderately thick layer of 

 horizontally disposed muscular fibres ; 4. Within this a 

 widely reticulated tissue terminating in follicular gland-cells, 

 closely aggregated and forming a layer internal to the wall 

 of the sac, fully one third of its diameter in breadth at the 

 median part (PI. XIII. fig. 9). A serial range of sections, 

 together with careful dissection of a single valve, will show 

 that the glandular sac is divided on its upper portion by a 

 fine partition into two chambers, both opening into the basal 

 portion of the sac, and that these are disposed one on either 



* Monographies d'Ecliinodermes, " Anat. du genre Echinus" p. 48. 



