HYDROID ZOOPHYTES. 9 
consisting of a dense mass of branching and anastomosing tubes (fig. 6). Each 
tube is covered with its own very thin sheath of perisarc (fig. 33) and there is no 
common sheath of coenosarc covermg the hydrorhiza as a whole, such as we find 
in the Podocorynidae. In the central parts of the hydrorhiza the tubes are closely 
packed, anastomose freely, and are disposed in several layers. At the periphery 
however the tubes are reduced to a single layer, become more dispersed, and 
anastomose slightly (fig. 3). There are three kinds of zooids. 
In the central part of the colony there are gastrozooids and blastostyles (gonozovids) 
(fig. 6); at the periphery, gastrozooids and dactylozooids (fig. 5). The gastrozooids 
(figs, 5 and 6, gz.) are 1-2 mm. in height. They exhibit a conical hypostome 
surrounded by a circlet of six to ten simple tentacles each about 0°5 mm. in leneth. 
The dactylozooids (fig. 5, d.) are short finger-like structures 0°25 mm. long by 
0°06 in diameter, terminating in a pad distally which bears a battery of nematocysts. 
The dactylozooids appear to be covered with a chitinous perisarc, but in sections 
it is seen to be extremely thin or absent at the distal extremity. We have some 
specimens with the nematocysts discharged, and there can be little doubt therefore 
that the battery is functional. These dactylozooids have no tentacles. The 
blastostyles are shorter than the gastrozooids, and usually exhibit neither mouth 
nor tentacles (fig. 6, b/.). There is always a short conical hypostome armed with 
nematocysts, and occasionally this is surrounded by a circle of four rudimentary 
tentacles (fig. 6, b/. t.). 
The body of the blastostyle is usually considerably dilated and has a 
superficial resemblance to a simple ovoid sporosac. 
Gonosome.—The medusoid structure of the gonosome is completely reduced 
in the male, but as no female blastostyles were found we can make no statement 
to the effect that the same is true of both sexes. The sperm cells (fig. 33, sp.) are 
found in a dense cluster between the ectoderm and endoderm even in the youngest 
blastostyles we have examined (0°1 mm. in length), and neither in these nor in the 
older blastostyles can we find any true medusoid structures. 
FAMILY PODOCORYNIDAE. 
In this family we include Podocoryne (Sars), Hydractinia (Allman), and other 
less well-known allied genera. The very interesting new genus //ydrodendrium 
(Nutting) may, we consider, be now included in this family, as the species //ydractinia 
dendritica connects it with the other species of //ydractinia. 
HypRACTINIA DENDRITICA. 
(Plate Il., figs: 7, 8, 9, 9a, 10.) 
Localities.—Specimen A: W.Q., March 21st, 1902; —10 fms. Specimen B: 
Locality unrecorded. Label lost. 
you. It. 2D 
