189 
bottom, the stronger muscles on the posterior side of the spine basis 
lending especial force to the backward movement of the spines, 
the animal thus being pushed forward through the ground). In 
the young specimens the areoles are comparatively large, confluent 
and make a very prominent feature. (Fig. 22 b). The miliary tubercles 
are confined to the narrow lines between the areoles and thus show 
a more or less distinet circular arrangement round the primary tub¬ 
ercles. Glassy tubercles are not found. 
I'ig. 22. Part of ambulacrum (a.) and (right anterior) interambulaerum (b.) of 
Echinobrissus recens ; from a specimen 11 mm long. Tlie ambulacral pores 
open obliquely on the plates, so as to be invisible except in oblique 
view ; they lie in the normal place, forming a straight series. 24 /i. 
In the interior anatomy it is noteworthy that fairly large inter- 
radial outgrowths are found on the watervascular ring, corresponding 
to the „Polian vesicles". The intestinal appendix is conspicuously 
folded, in the younger specimens it has, indeed, quite a remarkable 
Annelid-like appearance. The content of the digestive organs is 
remarkably coarse, consisting — besides smaller unbroken shells, 
Foraminifera — of fragments of shells, Bryozoa etc., so large that 
it is hardly intelligible how they could possibly pass through the small 
mouth. Evidently it must be capable of widening even to the borders 
of the peristome. 
The outstanding feature in the anatomy of Echinobrissus is, how- 
