PTEROBRANCHIA OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 441 



KXPLANATION OF PLATES. 

 PLATE I. 



Figs. 1-5. Selected pieces of colony <if i>y/// /<)<//.<//,< </<////.<>, n. sp., drawn by Miss (J. M. 

 WOODWARD. Natural size. Tlie specimen drawn in fig. 1 is selected .-is the type-specimen of tlie species. 



K II. 

 Cepkalodiscus <irj<jliilinun, \\. sp. 



The figures were drawn with the Zeiss objectives severally indicated, and were then reduced to two-fifths 

 linear. Tlie scale for the two objectives used in drawing the figures is given, in hundiedtba of a millimetre, 

 at the bottom of the plate. 



Fig. 1. A young bud. Ubj. A. 



Fig. 2. A slightly older Imd. Ol.j. A. 



Fig. :j. An older bud. Obj. A. 



Fig 4. A still older bud. Ol.j. A. 



Fig. 5. Obliquely frontal sec/linn. sh"\ving both testes (t./., /./.), parts of both gill-slits (g.t.), and the 

 left collar canal (c.c.). Obj. ('. 



Figs. 0-11. Frontal sections of one zooid. 



Fig. G. Showing eight of the left anus (as numbered) and seven nl the right arms. Obj. C. 



Fig. 7. Showing the same fifteen arms, the anterior dorsal horns nf the collar-cavities (li.c.-u.), the peri- 

 l-aid imn I/"-/-.) enclosing tlie pericardia! sinus m heart, and the internal openings nf the proboscis pi ires (/ >./>.). 



Obj.C. 



Fig. M. Showing the anterior end of tlie notochord (nrh.) and of the right lobe (u/>.r.) of the operculnm. 



Obj.C. 



Fig. 9. Through the mouth (>.). The dmible appearance nf the left lobe ("/'.I.) "t the ..percuhim i- 

 dnu to the fact that the organ in .pies! inn is folded ventrally. To see the correspondence between the two 

 sides of the section, the part of the left lobe which is nearer the proboscis (p.) must be imagined to have 

 been folded dursally. It would then not have appeared in the section, and the left lobe of the operculum 

 \\niild have had much the same appearance as the right lobe. Obj. C. 



Fig. 10. The month (m.) is still visible. The reflected part of the left lobe (op. I.} "I the "percidum is 

 almost separate from the rest of the organ. Obj. C. 



Fig. 11. Through the region of the collar-canals (c.c.) and gill-slits (</...). The right testis (/./.) is veiy 

 small in this zooid. Two of the terminal lobes of the scalloped edge of the right half (op.r.) of the operculnm 

 are visible. Obj. C. 



Fig. 12. Stomach (xtuin.), intestine (//.), lectnm (/.), and one testis (/.) of an old x.ooid. Obj. A. 



Fig. 13. Stalk, in transverse section. Olij. C. 



Fig. 14. Proboscis-stalk, in transverse, section, showing both proboscis-pores (/'._//.). the anterior dorsal 

 horns (b.c.-a.) of the collar-cavities, the anterior end of the central nervous system (<...-.), and the peri- 

 cardium (/"'''.) with the included pericardia! sinus. ( )bj. C. 



Fig. 15. Median sagittal section of the anterior end of a /.ooid, showing the imtoehnrd (nrli.). Obj. (_'. 



Fin. 1G. Nearly median sagittal section nf another zooid, showing the alimentary canal. Obj. C. 



N.B. In several of the sections, figured parts of tlie epithelia were somewhat macerated, as the result 

 of imperfect preservation. The epithelium of the stomach in fig. 16, part of the anterior epidermis of the 

 proboscis in figs. 6-9, and part of the epidermis containing the central nervous system in figs. 10 and 11 

 have accordingly been restored where necessary. 



(ROY. SOC. EDIN. TRANS., VOL. XUX., "ili.Vi. 



