1873.] DUNCAN GENUS PAI^OCOEYNE. 415- 



participate in its gentle movements, and also in the benefits accruing 

 from the currents in the water developed by the cilia of the 

 Polyzoon. 



It was evident that the ornamentation of the hydroid was 

 mimetic of that of the Polyzoon. 



Dr. Allman suggests (op. cit.) that the ornamentation and the 

 calcareous test do not resemble the structure of the covering of 

 Bimeria, that the opening on the distal end of the tentacles was 

 too small for the passage of a well-developed soft tentacle, and that 

 the chambered base is anomalous amongst the class. He considers 

 that the form should be associated with the Ilhizopoda. 



The lately discovered specimens indicate the manner of the 

 growth and development. 



In specimens consisting of a short stem and broad base without the 

 capitulum the stem does not appear to have been fractured, and it is 

 taj)ering in form and has a narrow superior orifice. 



Another specimen (PI. XIV. fig. 1) resembles those just mentioned, 

 but is taller. The stem has a branch which has been fractured. 



Other specimens (figs. 2 & 3) show that the upper part of the 

 capitulum close to or at the metastome is projected (1) in the form of 

 a closed prominence, or (2) as a stem-like continuation with a small 

 aperture on its distal end. 



When this stem-like continuation has grown to a considerable 

 length, the appearance of the whole organism is that of a long stem 

 with a central whorl of tentacles. 



Many specimens have very large bases. These cover many cells 

 of the Fenestella and the intermediate calcareous tissue. It is very 

 difficult to arrive at a satisfactory conclusion whether or not the 

 base is itself divided into cellular compartments. After due con- 

 sideration I feel disposed to believe that the wide and dactylose base . 

 incrusts the Fenestella, and that there is a space in the base which 

 is uneven and very irregular in shape, but not cellular *. The 

 shape and general complexity of this space are determined by the 

 outline of the Polyzoon beneath; and there do not appear to be 

 involutions or septum-like processes of the calcified periderm of the 

 Hydroid. 



It would appear from the examination of the specimens that the 

 form grew from the base at first without a hard capitulum and ten- 

 tacles ; that it branched in this condition, or had an offshoot 

 destined either to continue the same trophosomal structures, or give 

 rise to those of a different kind and belonging to the gonosome. 



The opening in the distal end of the nascent stem could admit of 

 the passage of a polypiform mass with all its tentacles. Under 

 such circumstances, the calcareous stem would be the periderm of 

 the hydrocaulus. The branch would terminate in the same manner 

 as the stem, or else would, under the theory of the Hydroidean 

 affinities of the animal, be the periderm of the gonosome. 



With growth, the more or less bell-shaped pofypite surmounting 



* The cellular appearance shown in Phil. Trans. 18G9, plate lxvi. fig. 4, is 

 due to the cells of the Fenestella. 



2e2 



