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ME. H. N. MOSELEY ON THE 
represented as seen when viewed from above with the microscope focused 
somewhat into the depths of the structure. A deep focus is necessary in 
order to reach the far-retracted zooids. The deeper reticulations of the 
hydrophyton are thus brought into view. 
MZ. Mouthed zooid. 
Z, Z. Mouthless zooids. 
Fig. 12. View of the inferior surface of the superficial living layer, from a specimen 
decalcified in chromic acid and viewed by reflected light. The figure shows 
the ramifications of the canals and vessels of the hydrophyton and their 
connexions with the zooids of one complete group or system. 
MZ. Under surface of mouthed zooid. 
Z. One of the seven surrounding mouthless zooids. 
C. Canal. 
B, B. Branches of this canal. 
B', B'. Secondary branches, from which and from B B arises a compli- 
cated network of finer vessels. 
Fig. 13. Enlarged view of a tentacle of a mouthless zooid. 
K. Spherical head of the tentacle filled with thread-cells of various 
sizes. 
E. Ectodermal layer. 
EC. Eamified cells or nuclei of the endodermal layer. 
M. Membranous layer. 
P. Pigmented cells within the cavity of the tentacle. 
C. Body-cavity continuous with that of the tentacle. 
Fig. 14. Diagram showing the arrangement of the muscular fibres in a mouthed zooid. 
The longitudinal muscles are gathered into bundles, which pass outwards for 
insertion on to the radially disposed vessels of the hydrophyton. Other fibres, 
less densely placed, occupy the interspaces between these bundles. 
O. Mouth of the zooid. 
A, A. Badially disposed vascular offsets from the base of the zooid. 
LM. Longitudinal muscular bundles. 
CM. Circular muscular fibres. 
Fig. 15. Transverse section of a mouthed zooid. 
E. Ectodermal layer, containing thread-cells in various stages of deve- 
lopment. 
M. Membranous layer. 
LM. Longitudinal muscular fibres seen in section as a series of dark 
points. 
G. Gastric cells. 
The narrow dark zone between the longitudinal muscles and membranous 
layer indicates a possibly existing circular muscular layer. 
