Fechter's contention is, furthermore, not consistent with the anatomy of the madreporite and its associated stone canal. The form of the madreporite does not suggest a simple "relief valve." In sea urchins the madreporite typically consists of 300-400 pore canals partially filled with cilia that tend to forcefully exclude particles (Tamori et al., 1996).
Attention was focused on pieces containing the madreporite complex, the aboral half of the stone canal, and representative parts of the aboral and oral body walls with tube feet and ampullae attached.
Substantial numbers were also found within the water vascular system, especially in the madreporite and stone canal [ILLUSTRATION FOR FIGURES 1-12 OMITTED].
Many of the particles that succeed in passing through the length of the pore canals become entangled in a string of material within the lumen of the stone canal [ILLUSTRATION FOR FIGURE 7, 8 OMITTED], which is lined with ciliated cells filled with granules (Rehkamper and Welsch, 1988).
The water vascular system is connected indirectly to the perivisceral coelom through an opening between the upper end of the stone canal and the adjacent axial sinus [ILLUSTRATION FOR FIGURE 13 OMITTED] (cf., Jangoux and Schaltin, 1977; Bachmann and Goldschmid, 1978).
Functional morphology of the stone canal in the sea urchin Eucidaris (Echinodermata: Echinoidea).
The region of the madreporite and stone canal (identified by the pigmentation pattern) was then surgically destroyed and sealed with a small cement plug.
Its duct points towards the first and away from the stone canal. This orientation suggests that the secondary pore may be a rejection pathway, but there is no way of verifying that.
Opposite this opening is the entrance to the lower end of the stone canal [ILLUSTRATION FOR FIGURE 8 OMITTED], which thus does not directly connect with the ampulla, but rather with the right axial sinus.
The four structures (the two separate parts of the axial sinus, the stone canal, and the axial organ) all rise in a long arch towards the ring complex located high up in the mouth frame.
At the same level in which the two parts of the axial sinus join, the top of the stone canal bends over and joins the ring canal that encircles the mouth [ILLUSTRATION FOR FIGURE 13 OMITTED].
This labeling diminished rapidly up the stone canal [ILLUSTRATION FOR FIGURE 20 OMITTED].