470 F. G. HEATHCOTE. 
Fic. 28.—Longitudinal vertical section through first post-cephalic segment 
of a slightly later embryo than Fig. 27. som. m. Somatic mesoderm. 
ec. Hetoderm., mem. ex. Membranous envelope. sp. m. Splanchnic meso- 
derm. cav. in mes. Cavity in mesoderm. (Zeiss, D.) 
Fic. 29.—Longitudinal vertical section through part of a tenth day embryo, 
to show ventral flexure. sp. m. Splanchnic mesoderm. som. m._ Somatic 
mesoderm. v./. Ventral flexure. (Zeiss; F.) 
Fic. 30.—Longitudinal vertical section through embryo rather later than 
Fig. 29, to show ventral flexure. ec. Ectoderm. mes. Mesoderm. v./. Ven- 
tral flexure. 
Fic. 31.—Transverse section through late tenth day embryo, to show ner- 
vous system. sp. m. Splanchnic mesoderm. som. m. Somatic mesoderm. ec. 
Ectoderm. ec. th. Ectodermal thickening. Jon. fur. Longitudinal furrow 
between nerve-cords. ex. Endoderm forming gut. (Zeiss, D.) 
Fic. 32.—Ventral part of a transverse section through an embryo of the 
eleventh day, to show the nerve-cord and the Malpighian tubes. This section 
is taken in the posterior region, about the sixth segment. som. mes. Somatic 
mesoderm. gl. Ganglia. Malp. ¢. Malpighian tubes. pr. Proctodeum: 
sp. mes. Splanchnic mesoderm. y.s. Yolk-spherules. v. ec. Ventral ectoderm. 
b.c. Part of body cavity between the nerve-cord and ventral ectoderm. 
(Zeiss, D.) 
Fic. 33.—Vertical longitudinal section through part of a twelfth day 
embryo, to show the stomodeum. sud. gi. Subcesophageal ganglion. suprae. 
Supracesophageal ganglion. s¢. Stomodeum. In this section the supra- and 
sub-cesophageal ganglia are not cut exactly in the middle line, and so appear 
smaller than they really are. (Zeiss, D.) 
Fic. 34.—Transverse section through a twelfth day embryo in posterior 
region of body. g/. Ganglia of nerve-cord. +. app. Rudiment of appendage. 
mes. Mesoderm forming a partition to the body cavity. pr. Proctodeum. 
Malp. t. Malpighian tubes. m. ez. Mesoderm cells in the body cavity derived 
directly from the endoderm. 
All the figures were drawn by myself under a Zeiss’s camera lucida. 
