448 A. A. W. HUBRECHT. 
Fie. 11.—Corresponds to Figs. 6 and 9. Participation of the mesoblast in 
the formation of brain and proboscis. The cavities of the posterior brain- 
lobes situated at the point of junction between the cephalic and ventral plates. 
Fic. 12.—A young larva that has stripped the coating of primary epiblast. 
Further development of proboscis, proboscidian sheath, and mesoblast in the 
head (brain-lobes). 
Fie. 13.—Corresponds to Fig. 12. Posterior attachment of proboscidian 
mesoblast. Cavity of proboscidian sheath and blood-course around the 
cesophageal part of the archiccelom. Coalescence of definite cesophagus with 
mid-gut. 
Fie. 14.—Corresponds to Figs. 12 and 13. First appearance of the lateral 
nerve stems in the mesoblast. 
Fic. 15.—Adult stage, transversely cut immediately behind the cesophageal 
region. The two lateral nerves, the three longitudinal blood-vessels, and the 
posterior parts of the nephridial char Is; the latter, as well as the intestine, 
rose-coloured. 
Reference for combining these s into seven successive stages of 
development to which they severally (7. stands for transverse, L. for 
longitudinal, H. for horizontal section 
Stage I—Fig. 1(7.). Stage IL—. .. Stage 1II.—Figs. 3 (7.), 
4(f.),7(L.). Stage lV.—Figs. 5 (2), 8 (L.),10(H.). Stage V.—Figs. 
6 (7), 9 (Z.), 11 (H.). Stage VI.—Figs. 12 (71), 13 (L.), 14 (H.). Stage 
VII.—Fig. 15 (7). 
