408 Baldu'in Spencer : 



EXPLANATION OF PLATES XX IV., XXV. 



Fig. L — General view from the side. The hiteral groove is re- 

 presented between the marginal bands 1 and 2. Marginal 

 band 4 is seen through the transparent jelly. 



Fig. 2. — A portion of the al)oral surface on a larger scale, to 

 show the conical elevation cut through by the groove, 

 the upper part of the main central canal with its four 

 bands of cells, the small aboral canal and the processes 

 forming the aboral organ close to the opening of the 

 canal into the groove. 



Fig. 3. — Oral view. The mouth is seen in the centre leading 

 directly into the central canal. The numbers 1, 2, 3, 4, 

 correspond in position to the marginal bands seen from 

 the side in Figure 1. The downward growth, conical in 

 form, of the angle associated with marginal band 1, pro- 

 duces the appt^araiice of asymmetiy which is probably 

 also accentuated by irregular contraction during pre- 

 servation. 



Fig. 4. — Diagrammatic transverse section across the middle of 

 the body. The marginal bands are numbered, as in the 

 other figures. The relative positions of the marginal 

 bands, lateral groove, ribbons of cells on the walls of the 

 central cavity, and the faintly marked septa ( I) are 

 shown. The latter are indistinguishable in sections, and 

 only visible in a few specimens. 



Fig. 5. — Downward conical process of one angle of the oral, and 

 the oral end of one lip of the lateral groove drawn on a 

 larger scale to show the serrations. 



Fig. 5a. — Portion of a marginal Ijand to show the '" cuticle " and 

 punctated material beneath. (Zeiss F. Oc. 2.) 



Fig. 6. — Part of one of the four riblion-like bands of cells on the 

 wall of the central cavity, together with the surrounding 

 cells lining the rest of the cavity. All are extremely thin, 

 the latter having much more definite outline than the 

 former. (Zeiss F. Oc. 2.) 



Figs. 7 and 8. — Sections across the aboral organ, showing the 

 canals that traverse it, and the regular arrangement of 

 the nuclei in the jelly of which it is formed. 



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