80 THE VOYAGE OF H.M.S. CHALLENGER. 



its full extent. The powerful volume of its contents is probably subject to important 

 modifications according to the state of contraction of its muscular and very extensible 

 subumbral wall. 



The inner or axial wall of the coronal sinus is firmly connected with its external or 

 abaxial wall at four interradial points. These points lie exactly in the radii of the four sense 

 clubs, in the middle third of the height of the sinus, a little above the middle (figs. 8, 12, 

 13, hi). They are the important septal nodes or fused nodes (" nodi septales, nodi 

 cathammales," hi; PL XX. fig. 8, hi; PI. XXI. fig. 17, hi; PI. XXIII. fig. 33; 

 PL XXV. fig. 8) ; they correspond to the interradial septa of the Lucernaridse and 

 Cuboruedusaa, which divide the length of their radial pouches. Each of the septal nodes 

 forms a gelatinous cube, tiny but firm as cartilage, of from 2-3 mm. in diameter. Under 

 strong magnifying power, the transverse section (PL XXV. fig. 8) shows that the 

 umbral gelatinous substance of the thick abaxial wall (wg) is firmly fused here with 

 the gelatinous supporting plate of the subumbral axial wall (ziv). Between the two 

 walls, however, in the tangential median plane of each node, there is a double layer of 

 endoderm cells, the important cathammal plate (" vascular plate or endodermal lamella," 

 dk). The higher cylindrical cells of the axial cell layer (dw. 2 ) form the direct continuation 

 of the subumbral endodermal epithelium of the inner sinus wall (dw) ; in the same way the 

 flatter cells of the abaxial cell layer (du 2 ) pass immediately into the umbral endodermal 

 epithelium of the external sinus wall (du), and contain the black-brown round pigment 

 granules by which the wall is characterised. We cannot, therefore, doubt that the nodes 

 are really formed by fusion of the two vascular walls. The gelatinous substance on 

 both sides of the double gastral lamella was so much hardened that it notched the knife 

 in making sections. Under stronger magnifying power (PL XXV. fig. 8) it showed 

 here the same striking induration and histological modification of the gelatinous tissue, 

 already described in the periphery of the lobe clasps, the transition into hard fibrous 

 cartilage (comp. above p. 67, and PL XXV. fig. 10). 



If we suppose that the four septal nodes, prolonged centripetally to the pylorus and 

 developed into four selvages, connect the axial and abaxial wall of the coronal sinus in 

 its entire proximal half, the sinus would thereby be divided into four wide perradial 

 pouches, corresponding to those of the Lucernaridse and Charybdeidae ; and as in these the 

 four radial pouches here communicate below by a circular canal, viz., by the simple distal 

 half of the circular sinus, below the septal nodes. We may therefore say the ideal 

 horizontal circular line, in which the four interradial sejotal nodes lie, form the boundary 

 line between an upper and a lower coronal sinus, both of which are in open communica- 

 tion between the four nodes. The upper or proximal coronal sinus (cs 4 ) corresponds to four 

 wide perradial pouches, whose septa are reduced to nodes, and which communicate by 

 the gastral openings with the central stomach. The lower or distal coronal sinus (cs. 2 ) 

 corresponds to a very much widened coronal canal which connects the four radial pouches 



