938 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
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I 
after the gonophore is partially formed, as Weismann and others have found to be the case in many 
hydroids. The male gonophore, as said before, differs from the female only in bearing spermatozoa 
instead of oya. (See fig. 6, pi. i.) 
In Hydra the ova are formed directly in the body wall of functional hydranths, and there is 
nothing {.hat can be called a true blastostyle as distinct from the hydranth itself. Here, however, 
each ovum is inclosed in a separate closed sack, develops a hard encasing wall around itself, and later 
develops a statoblast. 
It thus appears that the reproductive parts in the Hydra are in some respects more highly 
specialized than those found in Hydrodendrium. 
Relationships of the family Hydrodendridse. — Up to comparatively recent times there was but one 
known family of Hydroids that exhibited the peculiar character of having the skeleton composed of 
a chitinous network which was covered with a layer of coenosarc, and that was the family Hydractinidse. 
Prof. Louis Agassiz, with his usual clear insight, recognized the relationship between this family and 
the Milliporidse, the details of which have been worked out by several writers, including Professor 
Moseley. Since that time two other families having this characteristic have been described. One of 
these, the Ceratellidse a , was instituted in 1868 by Doctor Gray, who regarded it as a family of sponges. 
In 1888 Bale recognized its family rank and also that it was composed of true hydroids. In 1891 Prof. 
W. Baldwin Spencer, of Melbourne, discovered another remarkable form, Clathrozoon wilsoni, for which 
he instituted a new family, the Hydroceratinidse, in which the colony is branching, as in the Ceratellidse, 
but the superficial coenosarc is enveloped externally by a very thin chitinous layer that incloses the 
entire hydrocaulus. 
It thus appears that up to the present time no less than four families of Hydroida have been 
described having the common character mentioned above. The collection secured during the Hawaiian 
cruise of the Albatross contains two other species which, in my opinion, should form the types of two 
additional families of this group, making six in all, which may be characterized briefly as follows: 
Table showing the main points of resemblance and difference between the families of Hydroida having the 
common character of stems composed of a chitinous (in one case calcareous) framework overlaid with 
naked coenosarc. 
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i 
General character of 
colony. 
Origin of 
hydranths. 
Form of hydranths. 
Defensive 
“persons.” 
Gonosome. 
HYDKACTINIDjE ... 
An encrusting mass. 
Spines present. No 
hydrophores. 
From several ccen- 
osarcal tubes. 
One circlet of fili- 
form tentacles. 
Proboscis pres- 
ent. 
Spiral zooids. 
Borne on modified 
hydranths. Ma- 
nubrium present. 
CERATELUDjE 
Branching. No 
spines. Hydro- 
phores composed 
of basket-like open- 
work. 
From several ccen- 
osarcal tubes. 
Scattered capitate 
tentacles. Pro- 
boscis present. 
None. 
Medusoid gono- 
phores springing 
directly from the 
hydrocaulus. 
Hydrodendrid.e . 
Branching. Neither 
spines nor hydro- 
phores. 
From several ccen- 
osarcal tubes. 
One circlet of fili- 
form tentacles. 
No proboscis. 
None. 
Gonophores in form 
of hernia-like 
open sacks on 
body of unmod- 
ified hydranth. 
Tubidendrid.e 
(A new family 
to be described 
later.) 
Branching. Pseudo- 
hydrophores hard- 
ly evident. 
From a single 
ccenosarcal 
tube. 
Two circlets of fil- 
iform tentacles. 
Proboscis pres- 
ent. 
Finger-like naked 
processes. Ap- 
parently no 
nematocysts. 
Unknown. 
Hydrocerati- 
NIDjE. 
Branching. Tubular 
hydrophores pres- 
ent. Entire hydro- 
caulus covered 
with thin chitinous 
membrane. 
From several coen- 
osarcal tubes. 
One circlet of fili- 
form tentacles. 
Proboscis pres- 
ent. 
Nematophores 
with evident 
sarcostyles. 
Unknown. 
Milleporidjj 
Massive or branch- 
ing. Skeleton cal- 
careous. 
From several ccen- 
osarcal tubes. 
One circlet of cap- 
itate tentacles. 
A low proboscis. 
Daetylozooids 
with scattered 
capitate tenta- 
cles. 
Medusoid gono- 
phores in am- 
pullae. 
a The original spelling Ceratelladae is here changed to conform to the A, 0. U. code and to the practice of nearly all 
zoologists. 
