DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 119 
Fic. 11.—Transverse section of proboscis cavity. Mesoblastic elements 
distributed nearly uniformly all round the interior. 
Fie. 12.—Portion of these mesoblastic elements more highly magnified, to 
exhibit the differentiations. 
Fic. 13.—Section taken behind Fig. 11. The mesoblastic layer is thinner 
dorsally than elsewhere. 
Fig. 14.—In this section the septum separating the two horns of the cavity 
is reached. 
Fic. 15.—Still further back the first rudiment of the proboscis gland is 
reached (cp. Fig. 29). 
Fie. 16.—The rudiment of the gland lying in the septum more highly 
magnified. 
Fic. 17.—Section across the proboscis stalk. The anterior end of the 
notochord is reached. The back of the gland is nearly passed. The meso- 
blastic horn of the left side is apparently divided into two parts, this appear- 
ance is due to shrinking. 
Fig. 18.—The lumen of the notochord is reached. The extreme ends of the 
two anterior mesoblastic horns and the posterior apex of the left horn from 
the first cavity are all cut in this section. (The irregular folds of skin 
are due to the contractions of the body; it will be understood by comparing 
the figures of the whole animal that only the central part within the folds is 
the real stalk of the proboscis.) 
Fic. 19.—The section crosses the end of the archenteron, lying in front of 
the mouth. (The whole of this part of the archenteron becomes eventually 
pushed forward to form the notochord.) 
Fic. 20.—The mouth is here traversed, as also the anterior end of the 
nervous system. (A space, due probably to shrinking, is visible in the dorsal 
mesentery.) 
Figs. 21—29 are transverse sections of a larva, slightly older than the fore- 
going. Fig. 25 was drawn under Zeiss’s Immersion 2 and oe. 2; the others were 
drawn under Obj. D and oc. 2. They are numbered from before backwards. 
Fie. 21.—Section taken just behind the mouth, The lumen of the noto- 
chord is here shut off from the archenteron. 
Fic. 22.—The notochord still open to the archenteron. 
Fic, 23.—The nervous system is attached to the skin. 
Fic. 24.—The nervous system is already nearly separated from the skin. 
Fic. 25.—Part of the foregoing enlarged, to show the peculiar pyriform 
cells of the splanchnopleure (2). 
Fic. 26.—Nervous system still in the skin, 
Fic. 27.—The nerve-cord is separated from the skin. 
Fic. 28.—Two parts of the middle body cavities may be here seen separat- 
ing from the rest, probably forming part of the perihemal cavities, 
