A COLLECTION OF HYDEOIDS. 281 



slender (fig. 11). At the base of the polyp there is a charac- 

 teristic dilatation which is covered by a continnation of the 

 perisarc of the hydrocanlns (fig. 12). The proximal or basal 

 tentacles are of considerable length and are about 17 in 

 nunilier ; the distal or oral tentacles are short and are about 

 14 in number. 



The total height of the polyp^ measured to the base of the 

 dilatation, is about 2"51 mm., the greatest breadth, measured at 

 the level of the basal tentacles, is about 1*21 mm. The height 

 of the dilatation is about 0'55 mm., and its width 0"61 mm. 



Gonosome. — The gonophores are budded in irregular clusters 

 on semi-erect peduncles {j^d.) or blastostyles, which spring from 

 the hydranth just above the basal verticil of tentacles. The 

 gonophores reach a high state of development ; marginal ten- 

 tacles, radial and circular canals, and a velum (r.) are present. 



The gonophore figured (fig. 12) is a young male, but owing 

 to the lack of matei'ial older stages have not been seen. A 

 female gonophore has not been found, and consequently the 

 nature of the actinula is undetermined. 



(leneral histology. — A vertical section of a hydranth is 

 represented in fig. 12, PI. XLYI. At the upper edge of the 

 basal dilatation the ectoderm is conspicuoiisly thickened, and 

 on its under side there is a shallow groove {'p.g.). The peri- 

 sarc of the hydrocaulus is continued up into the groove, and 

 then fades away on the rounded surface of the thickened 

 ectoderm. The perisarc of the hydrocaulus consists of an 

 inner and outer layer, the later being continued over the base 

 of the hydranth. 



The nematocysts in the ectoderm are mostly small and 

 inconspicuous; they measure about 5"1 ^ in length and 4/i 

 in breadth {s.ii.). In the endoderm there is a larger variety 

 [l.n.) measuring 8'3 fx and 7'9 fi respectively. 



The endoderm around the mouth contains, as usual, nume- 

 rous deeply staining nuclei ; the oral or distal tentacles are 

 provided with septate skeletal endoderm. The vertical sides 

 of the hydranth have a very thin endoderm Avith a few 

 vacuolated cells {v.c), and also large nematocysts. The base 



