HYDEOID ZOOPHYTES. 11 



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 number 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 • 6 mm. in length. Proximally to the jegion where the immature 

 zooids and gastrozooids occur there is a region with numerous ripe blastostyles 

 (fig. 8, hi.), 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 • 1- 

 • 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 • 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 diff"erences between the basal 

 part of "specimen A and specimen B which might be regarded by some authors to be 

 of sufiicient 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 H. echinata 

 and other species. 



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