TWO SPECIES OF HYDRACTINIA 
487 
single section (=7.5ifi) in a nearly ripe gonophore examined for 
the purpose, the original communication being mostly cut off 
by the formation of a membranous septum of supporting lamella. 
It may also be remarked that the position of this opening may be 
apical or eccentric both in young and mature gonophores. The 
larger part of the contents of the gonophore at this stage con- 
sists of the germ cells which have become very small by repeated 
divisions. Numerous karyokinetic figures are however present, 
showing that the process of division is still actively going on. The 
figures probably belong to maturation stages. Careful observa- 
tion shows the presence of the nuclei of the inner ectoderm cells 
here and there between the sperm cells, distinguishable by their 
smaller size, more or less elliptical shape and especially by their 
deeper and diffuse staining. The ripe male gonophores are, as 
already mentioned, slighth^ ellipsoidal in shape. 
Relationships with other forms 
In regard to the soft parts nothing particular need be said on the 
relationships of the present species, but the skeleton appears to 
lead us to a better understanding of some of the forms previously 
described, including certain fossil ones. Of the species having 
skeletons of the same general structure as H. sodalis, Stechow" 
mentions Hydractinia calcarea Carter,-^ Hydractinia angusta 
Hartlaub ('04) , Hydractinia dendritica Hickson & Gravely, Hydro- 
dendrium gorgonoide Nutting^^ and Clathrozoon wilsoni Spencer.^e 
Again Nutting" mentions the following families as being more or 
less closely related: Hydractinidse, Ceratellidse (Solanderidae), 
Hydrodendridse, Tubidendridae (a new family to be described), 
Hydroceratinidse and Milleporidae. It seems to me that of the 
described species of Hydractinia, H. arborescens Carter is most 
nearly related to H. sodalis, if indeed it is not identical with the 
latter. Carter^^ had a single specimen of this species which ^'now 
"Loc. cit.: '09, p. 22. 
2* Hickson & Gravely: '07, p. 9. 
Spencer: '90, p. 123. 
» Carter: '77, p. 50. 
25 Nutting: '06, p. 936. 
cit.: '06, p. 938. 
