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Parker. — Metridium marginatum, 
EXPLANATION OF PLATE. 
All figures represent transverse sections of the column of Metridium marginatum 
Milne-Edwards. In each case all the complete mesenteries have been drawn, and 
in some instances a few of the incomplete ones. All figures are magnified about 
1.5 diameters. 
Fig. 
Fig. 
1. 
2. 
Diglyphie specimen, showing typical hexamerous arrangement of the 
complete mesenteries, and a regular group of subordinate mesen- 
teries in a primary exocal. 
Diglyphie specimen, showing a very irregular arrangement of the com- 
plete mesenteries, one group of which resembles the crowded group 
of mesenteries found opposite the directive pole in the monoglyphie 
type. In this crowded group occurs an unpaired mesentery (x or y). 
Monoglyphie specimen, with five pairs of non-directives, showing the 
regular arrangement of the subordinate mesenteries about tie pair of 
non-directives opposite the directive pole. 
Monoglyphie specimen, with six pairs of non-directives, showing the 
regular arrangement of the subordinate mesenteries about the two 
pairs of non-directives opposite the directive pole. 
Monoglyphie specimen, with ten pairs of non-direetives, showing the 
crowding of the non-directives in the region opposite the directive 
pole. 
'Triglyphie specimen. 
Monoglyphic specimen, showing pairs of mesenteries in which dorsal as 
well as ventral components are incomplete. 
Monoglyphie specimen, showing the union of two primary mesenteries. 
UT I , g 
