—.-” * 
4 
( 641 ) 
In consequence of these considerations the only course to adopt 
is to regard Ptilocodium as the representative of a new family. 
The above piece of work was undertaken at the suggestion of 
Professor Hickson, to whom I wish to express my sincere thanks 
for his most generous advice and assistance. 
mA) 
EXPLANATION OF PLATE. 
aut — autozooid of Ptilosarcus. 
bas coen. — basal coenosare of hydroid. 
dact. — dactylozooid of hydroid. 
ect. — ectoderm. 
ect. man — ectoderm of manubrium. 
end. — endoderm. 
end. can. — endoderm canal. 
end. lam. — endoderm lamella. 
end. man — endoderm of manubrium. 
gast. — gasterozooid of hydroid. 
gon. — gonozooid of hydroid. 
mes. — mesentery of autozooid of Ptilosarcus. 
nem. — nematocyst. 
ov. — ovum of Ptilosarcus. 
rad. can. — radial canal. 
spic. — spicule. 
stol. — growing tip of stolon. 
sub. ect. — ectoderm lining the cavity corresponding to the sub- 
umbrella cavity of a medusa. 
sup. ect. — superficial ectoderm of gonophore. 
fent. — tentacle. 
t. p. — tentacles of Pennatulid. 
External view of parts of two successive leaves of the Pennatulid, 
shewing the extent of the surface of the leaves, affected by the hydroid. 
Drawing of a microscope preparation of part of the free edge of a 
leaf of Ptilosarcus, shewing the hydroid running out over the spicular 
projections of the autozooids X 20. 
Drawing of a preparation similar to >< 68. 
Longitudinal section of a Pennatulid leaf shewing the hydroid growing 
over the free edges of the leaf. 
Vertical section of basal coenosarc of the hydroid shewing superficial 
and lower ectoderms, and endoderm canals. 
Optical section of dactylozooid of hydroid shewing solid endoderm, and 
the characteristic four tentacles. 
Longitudinal section of gonozooid arising from base of gasterozooid, 
Transverse section of gonozooid. 
