HYDROID ZOOPHYTES. 1] 
gastrozooids and blastostyles at the base of the stem are very similar to those of the 
basal encrusting part of the colony, but distally the gastrozooids are smaller and 
apparently less contractile, and blastostyles are absent. 
Specimen B.—Assuming that the pieces in the bottle containing this specimen 
all belong to one colony, we have estimated that the height of the colony must have 
been at least 150 mm. There is no encrusting basal support as in specimen A, and 
the axes of the branches do not show any foreign hydroid or other kind of core. The 
branches arise irregularly and anastomose freely (fig. 10). They are circular in section, 
remarkably smooth on the surface, and their maximum diameter is about 3 mm. 
They are therefore much longer and thicker than the upright branching stem of 
specimen A, and we may add presumably older. Although there is no true basal part 
similar to that of specimen A, the encrusting habit is seen in places where sponge 
spicules and other foreign bodies have been overgrown by the colony. 
The skeleton is composed of a series of parallel intercommunicating chitinous 
tubes, the superficial tubes being externally incomplete, but there are no definite 
ridges or spines on the surface as in the basal part of specimen A. 
On the larger branches there appear to be no zooids at all. At the distal ends 
there are numerous small immature zooids which may become either gastrozooids or 
blastostyles, as well as a considerable nymber of gastrozooids. These gastrozooids 
(fig. 8, gz.) are about 1°5 mm. in height, and therefore slightly smaller than the 
majority of the gastrozooids of the basal part of specimen A. The mouth is on a 
conical hypostome which is surrounded by a series of filiform tentacles, 6-10 in number, 
and each one about 0°6 mm. in length. Proximally to the region where the immature 
zooids and gastrozooids occur there is a region with numerous ripe blastostyles 
(fig. 8, bl.), and only a few gastrozooids. These blastostyles vary from 0°3 to 0°7 mm. 
in height, but the majority are larger than those of A. They have 4-8 tentacles 0° 1- 
0°2 mm. in length, and have in some cases a minute mouth. The blastostyles each 
bear from 1—5 sporosacs (fig. 7, gph.) which in our specimens were all male, and when 
ripe about 0°3 mm. in diameter. The sporosacs are borne just above the base of the 
blastostyle. The branch shown in fig. 7 is somewhat intermediate in character between 
the region of gastrozooids alone and the typical region of blastostyles. 
In comparing the two specimens we notice certain differences between the basal 
part of specimen A and specimen B which might be regarded by some authors to be 
of sufficient importance to necessitate their separation into distinct species. Thus, the 
surface of B is smooth, of the basal part of A ridged ; the gastrozooids are smaller in 
B than in A; the blastostyles of, B are on an average larger than in A, and have a 
larger number of longer tentacles; the sporosacs of B are larger and less numerous 
than those of A, and are situated above the base, and not at the base, as in A. More- 
over in B the skeleton has the form of a series of parallel but communicating tubes, 
whereas in A it has the same irregular lacunar arrangement that is found in //. echinata 
and other species. 
2D 2 
