Asymmetron bassanum, Gilnther. 89 



EXPLANATION OF PLATES. 



In* all figures 



B. C. Coelom. 



D. F. C. Dorsal tin chambers. 



E. S. Eye spot. 



F. S. Fin space. 

 MY. Myotome. 

 N. C. Nerve cord. 

 NT. Xotochord. 

 O. C. Oral cirri. 

 O. H. Oral hood. 



O. P, Olfactory pit. 



PI. Pigment. 



P. R. Pigment ring. 



Plate XVIII. 

 Fig. 1 — Transverse section through region of atriopore, 



showing atrial cavity extending between coelom 



and body wall except in mid-dorsal region. 

 ,, 2-6 — Transverse sections behind atriopore. 

 ,, 2 — Atrial cavity still separating coelom from body wall 



except dorsally. 

 ,, 3 — Atrial cavity divided into two caecae, right and left. 



,, 4 — Showing right and left atrial caecae — the left close 



to its termination. Ventral fin ray also shown. 

 „ 5 — Left atrial caecum has disappeared completely. 



,, 6 — Termination of right atrial caecum. 



J, 7 — Transverse section through region of anus. Atrial 



cavity has completely disappeared. 



Plate XIX. 



Fig. 8 — Diagrammatic longitudinal section showing (1) 

 atriopore, (2) anus, (3) coelom extending poster- 

 iorly on either side as far as the anus, (4) right 

 and left atrial caecae extending posteriorly between 

 coelom and body wall. 

 J, 9 — Diagrammatic longitudinal horizontal sections of 



ventral fin rays cut at various angles. 



