PLATE II. 



Figs. 1-7. Young colonies of Fyi'osoma. 



Fig. 8. Pyrosoma elegans (?). 



Figs. 9-15. Pyrosoma S2)inosum, n. sp. 



at. Atrial aperture. 



hr. Branchial aperture. 



c.cl. Common cloacal aperture. 



d.t. Dorsal tubercle. 



m.b. Muscle baud. 



n. Nerve. 

 n.g. Nerve ganglion. 

 K.gl. Subneural gland. 



Fig. 1. Very young colony of Pyrosoma, from Atlantic, April 12, 1876 ; slightly 

 enlarged. 



Fig. 2. Closed end of same colony in surface view (S. 1). 



Fig. 3. Open end of same colony in surface view (S. 1). A'-A"*. Areas occupied by 

 the four Ascidiozooids. 



Fig. 4. Optical section through the middle of same colon)', showing four young 

 Ascidiozooids (S. 1). 



Fig. 5. More advanced young colony of Pyrosoma from surface of South Atlantic ; 

 natural size. 



Fig. 6. Diagram showing the arrangement of the Ascidiozooids in this colony, as seen 

 from closed end. A'- A*. Four large central Ascidiozooids ; B'-B". Eight 

 smaller ones at open end ; C-C*. Four smallest ones at closed end. 



Fig. 7. Same colony magnified (Ross' binocular, 1^ in.). 



Fig. 8. Small colony of Pyrosoma elegans (?) (specimen B.) from the West Pacific, 

 March 16, 1875 ; natural size. 1, 2, 3, 4 indicate the positions of the four 

 Ascidiozooids forming the closed end of the colony. 



Fig. 9. Part of the surface oi Pyrosoma spinosum, n. sp., showing the spines; natural 

 size. 



Fig. 10. Three spines and branchial apertures of same ; enlarged. 



Fig. 11. Small part of surface of Pyrosom,a spinosum,, showing anterior ends of 

 Ascidiozooids ; natural size. 



Fig. 12. Part of internal surface of colony of same, preserved in picric acid, showing 

 the atrial apertures ; natural size. 



Fig. 13. Nerve ganglion and neighbouring parts of Pyrosoma spinosum; highly 

 magnified (Zeiss' obj. D., oc. 4). 



Fig. 14. Ciliated cells from branchial sac of same; highly magnified (Zeiss' obj. D., 

 oc. 4). 



Fig. 15. Testis and vas deferens oi Pyrosoma spinosum (S. 1). 



