STRUCTURE 



237 



two latero-ventral, and one ventral. In the remaining segments 

 each ring has only three plates, one dorsal and two ventral, the 

 two latter being sometimes more or less fused in the last or ventral 

 segment. These plates all overlap from before backwards. 



As the name Echinoderes implies (Thorn-skin), the cuticle 

 is produced into points, bristles, or spines. The last segment 

 frequently bears a large pair of these, which have been compared, 

 on the flimsiest grounds, with the furcal processes of Crustacea 

 and the perforated toes of Eotifers and Gastrotricha. 



The proboscis when extruded has the form of a truncated 

 cone, obscurely divided into two segments, a ring of strong spines 

 marking the boundary between them, and a second double ring 

 of spines surrounding the apex. The eversion is of the type 

 termed by Lankester pleurembolic or acrecbolic, the sides being 

 first withdrawn, the apex first extruded. 



As in so many Invertebrata, the epidermis is not separated 

 by boundaries into distinct cells. This layer sends out processes 

 each of which lies in a hollow in the thick cuticle, and perforates 

 it to end in a fine bristle. Minute orange pigment -granules 

 occur at irregular intervals in this hypoderm. 



The muscles of Echinoderes are simple striated bands. 

 Numerous bands lie within and attached to the body- wall, extend- 

 ing its whole length ; paired dorsi- ventral muscles separate the 

 intestine from the reproductive organ on either side, and a 

 complex system effect the movements of the proboscis. 



Alimentary Canal. The pore at the tip of the proboscis 

 leads into a short thin-walled tube, which is rarely evaginated ; 

 into the base of this tube projects the short bluntly conical apex 

 of the large ovoid muscular pharynx (or gullet ?) ; this is lined 

 by an epithelial layer of nucleated protoplasm, which secretes a 

 strong cuticle. The stomach is a wide tube, somewhat dilated 

 in each segment between the paired dorsi-ventral muscles, and 

 tapering behind to end in the terminal anus. Four minute 

 glands open at the- junction of the pharynx and stomach. 



Kidneys. These are a pair of blind pear-shaped sacs, 

 ciliated within (the only case of ciliation in Echinoderes), lying- 

 in the eighth segment, and opening by the taper ends right and 

 left on the back of the ninth segment. 



Nervous System. All that has been clearly defined of this 

 is a small brain or ganglion lying dorsally at the junction of the 



