( 638 ) 
Dactylozooids. 
The dactylozooids are very numerous compared with the gastero- 
zooids. They occur at irregular intervals; there seems to be no defi- 
nite relation, as regards arrangement on the basal coenosarc, between 
the dactylozooids and gasterozooids such as we find in Millepora or 
Stylaster. 
The dactylozooids are short and broad and each bears four capi- 
tate tentacles crowded with large nematocysts (fig. 6). The zooids do 
not vary much in size, the average size being .186 mm. >< .106 mm. 
The smallest zooids measure .106 mm. X .053 mm. The capitate 
tentacles are .038 mm. in length and .033 mm. broad. The nema- 
tucysts of the tentacles are of the larger of the two kinds possessed 
by the hydroid and measure .017 mm. X .008 mm. The ectoderm of 
the remainder of the zooids shews no nematocysts. The endoderm of 
the dactylozooids and tentacles is solid and scalariform, there being 
no trace of a cavity or oral opening. (fig. 6). Judging from the 
preserved specimens the dactylozooids seem little, if at all, contractile. 
Gonozooids. 
The gonophores which are adelocodonic, arise in each case, as 
before described, from the base of a gasterozooid. Thus the base of 
a gasterozooid functions as a blastostyle (fig. 7). 
The gonozooids vary little in size, the average being .3873 mm. X 
186 mm. They are considerably reduced in structure, having the 
form of closed sporosacs. All the gonophores on the two specimens 
received are female. The ova are borne between the ectoderm and 
endoderm of the manubrium and have a diameter of .017 mm. They 
are practically all of the same size but it cannot be said whether or 
not they are ripe. 
The superficial ectoderm of the gonozooid and the ectoderm lining 
the cavity corresponding to the sub-umbrella cavity of a medusa, are 
separated by an endoderm lamella, which shows traces of radial 
canals (figs. 7 and 8). There is no velum and there are no sense 
organs and only traces of four rudimentary tentacles. Nematocysts of 
the smaller kind occur in the superficial ectoderm of the gonozooids. 
The Relation between the Hydroid and Ptilosarcus. 
The specimens of Ptilosareus sinuosus on which the hydroid is 
growing seem practically unaffected by it. The autozooids are well 
developed, showing no signs of degeneration. | 
The hydroid spreads only over the oral ends of the autozooids, 
that is, it keeps near the tentacles of the same, and does not run 
far over the leaves of the Pennatulid. Correlated with this is the 
