HYDKOID ZOOPHYTES. 5 



attached to the stems of Halecium arhoreum. The character of the bottom on which 

 its support grows is described as stony, gravelly, or very rough ground (Flagon Pt.). 



The species differs from most of the species of Perigonimus in having Ifixed 

 gonophores. 



On this account it might be placed by some authorities in Allman's genus 

 Wrightia, but for reasons that have recently been urged by Motz-Kossowska 

 (17 : pp- 68-71) we are of opinion that Wrightia should be merged with Perigonimus. 

 In this particular case the reasons for disregarding the genus Wrightia seem to be 

 particularly strong. The size of the colonies and of the individual zooids being much 

 greater than in the only known species of Wrightia, the specimens would, in the 

 absence of the gonophores, be undoubtedly referred to the genus Perigonimus. If 

 Perigonimus shares the power or possibility that some other genera of gymnoblastic 

 hydroids undoubtedly possess of variation in the character of the liberation of the 

 gonophores, being in some cases phanerocodonic and in others adelocodonic, we should 

 at least expect that the adelocodonic variation or condition would occur in specimens 

 living in an arm of the sea such as McMurdo Bay, that is for so many months in the 

 year covered with ice. 



Hydrosome. — From the ramifying hydrorhiza attached to the Halecium several 

 unbranched or occasionally slightly branched hydrocauli arise (fig. 1). They attain to 

 a height of about 8 mm. Many of the hydrocauli appear to be simply unattached 

 branches of the hydrorhiza, and even the pedicels of the gonophores occasionally give 

 off branches of indefinite function and power of growth. 



The transition from hydrocaulus to hydranth is gradual, the length of each 

 hydranth being about 1 mm. The hypostome is conical and is surrounded at its base 

 by a circlet of about 10 filiform tentacles each about 0*6 mm. in length. The 

 perisarc is continued as an exceedingly thin film over the hydranth as far as the base 

 of the tentacles. The hydranths vary considerably in shape (fig. 3) and are probably 

 very contractile. 



Gonosome. — The gonophores are situated on short pedicels which, in the case of 

 the female, are thickened distally. The colonies appear to be invariably dioecious. 

 In both sexes the gonophore is a degenerate medusa. In both sexes the gonophore 

 is protected by a thin layer of perisarc. It is larger in the female than in the male 

 (1-1 mm. X • 9 mm. in the female, and • 9 mm. x • 7 mm. in the male). 



In the female gonophore there is a large sub-umbrella cavity (fig. 3, su.c), the 

 manubrium is well developed and has a well-marked endoderm cavity. 



In the young gonophore there is a distinct endodermal layer of cells and 

 mesogloea in the umbrella, but in the adult gonophore (fig. 32) these are reduced 

 to a non-cellular mesogloea except at the margin, where a cord of cells represents 

 the ring canal. There are no radial canals in the adult gonophore. 



In the male gonophore the sub-umbrella cavity is completely filled with sperm 

 cells (figs. 2 and 32, sp.). 



