460 WILSON. 
EXPLANATION OF PLATE XXI. 
Figs. 82, 85, from Z. fetidus ; Fig. 83 from L. terrestris ; the others from LZ. communis. 
Fic. 79. Sagittal section of anterior part of an embryo shortly after the appearance 
of the head-cavity and the union of the cephalic ganglia. The remains of the 
Schluckzellen shown at S.Z. *K 225. 
Fic. 80. Corresponding sections through a later stage, in which the first pair of 
ccelomic cavities have come together behind the cephalic cavity at ca, the first dis- 
sepiment shown at D. X 225. 
Fic. 81. Sagittal sections through a still later stage, in which the cephalic ganglia 
have separated from the ectoblast and begun to travel backwards; the prostomial 
cavity is nearly filled with a network of mesoblastic cells; the cesophageal gland 
cells at g7. < 225, 
Fic. $2. Sagittal section of young embryo of Z. fetidus to show the thickened 
lower lip s. Z. of the stomodzeum. 225: 
Fic. 83. Longitudinal section through the nephric cord and developing nephridia, 
showing their relation to the dissepiments and coelomic cavities. X 400. 
Fic. 84. Corresponding section through Z. communis. X 400. 
Fic. 85. Surface view (from within) of developing nephridia and setigerous gland. 
The lateral limits of the nephric cord are defined by the longitudinal muscular 
bundles (72. ¢.). X 700. 
Fic. 86. Longitudinal section through developing nephridia (somewhat older than 
in Fig. 84), and setigerdus glands, showing their relations to the nephric cords, etc. 
The section is slightly oblique, and passes in front into a longitudinal bundle of muscle- 
fibres (mm. ¢.) (which now overlaps the margin of the nephric cord). X 400. 
Fic. 87. Longitudinal section through still older nephridia. X 400. 
Fic. 88. Corresponding section of a later stage, in which the setz can be dis- 
tinguished. The nephric cord can no longer be made out in front. X 400. 
(All the figures with the camera.) 
