DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 117 
6. Kowatevsky, A.—‘ Anatomie des Balanoglossus,” ‘Mem. Acad. Imp. 
Sci.’ St. Petersburg, 1866. 
7. LanxesterR, B, Ray.— New Points in Structure of Amphioxus,” 
* Quart. Journ. Micr. Sci.,’ xv, p. 257. 
8. Merscunrkorr, E.—“ Ueb. d. Metam. einiger Seethiere,” ‘Z. f. W. Z.,’ 
20, 1870. 
9. Murscunixorr, E.— Ueb. d. Syst. Stell. v. Balanoglossus,” ‘Zool. 
Anz.,’ 1881. 
10. Scorr, W. B.—* Beitrage z. Entw. d. Petromyzonten,” ‘ Morph. Jahrb.,’ 
Bad. vii. 
11. Spence, J. W.— Bau. u. Entw. v. Balanoglossus,” ‘Tag. d. Naturf. 
Ver.,’ Miinchen, 1877. 
12. Spencen, J. W.—*Z. Anat. d. Balanoglossus,” ‘ Mitth. a. d. Zool. Sta. 
z. Neapel.,’ Bd. v, Hft. 3 and 4. 
EXPLANATION OF PLATES IV—IX, 
Illustrating the “ Later Stages in the Development of 
Balanoglossus Kowalevskii, with a Suggestion as to 
the Affinities of the Enteropneusta.”? 
Complete List of Reference Letters. 
a. Anus. Ac. Archenteron. A/. Alimentary canal. a. 7. Anal lappets. 
bc.1, 2, 8. The anterior, middle, and posterior body cavities respectively. The 
letters Z and 7 affixed to these letterings denote that the parts are of the left 
or right side. 47. Branchial chamber. C. Apical tuft of cilia. C. WV. S. Cen- 
tral nervous system. c.g. Groove between the collar and the trunk. cil, 
Transverse band of cilia. Cl. Collar. CU’. The posterior fold of the collar, 
which eventually forms the operculum. C7/.sé. Skinof collar. D. 4. v. Dorsal 
blood-vessel. D. mes. Dorsal mesentery. D. x. s. Dorsal nervous system. 
dig. Digestive tract of alimentary canal. #. Ectoderm. ex. g. Refractive 
granules in mesoblastic cells. /- Mesoblastic fibres. g.s, Gill-slit. g.s.7. 
Branchial supporting rod. g/. Proboscis gland. gi. s. Sac of proboscis gland. 
gn. Ganglion (?) cells. #. Hypoblast. At. Heart. nt. Intestine. 1. 7. 
Lateral rods of the skeleton. 7. Lumenof notochord. I’. M". M'. Meso- 
blast derived from the anterior, middle, and posterior pouches respectively. 
Mo. Mouth. msc. Muscle-fibres. mz. Mucous gland. z.s. Nervous system 
n. enl. Neural canal. We. pr. Pore by which the notochord lumen opens into 
