20 Mr. E. Kirkpatrick on 



dilating at the nodes of the network into expansions, whence 

 arise erect, tubular, branchino- (?) zooecia. Zooecia very tall, 

 opaque, contracted at base, where they joined the expansions 

 of stolon. Height of fully developed zooecia 4*6 millim. ; 

 breadth from '16 to '2 raillim. ; breadth of stolon "02 millim. 



C. altum is closely allied to C. giganteum, Busk (Quart. 

 Journ. Micr. Sci. vol. iv. p. 93, pi. v. figs. 1, 2). In C. 

 altum the zooecia are higher and narrower than those of C. 

 giganteum and are contracted at the base. C. altum more 

 nearly resembles C. dilatatum as regards the characters of the 

 stolon. 



The respective dimensions of the zooecia of these three 

 species are as follows : — 



Length. Breadtli. 



C. giganteum 3-5 0-20-0-25 



C. dilatatum 0-9 0-13 



C. altum 4-6 O-lG-0-2 



In the absence of more specimens it would be rash to 

 assume that the " branching " in G. altum is a normal and 

 constant condition of that species, and not a mere sport. The 

 reasons for caution are, firstly, that several cells of the soli- 

 tary specimen of C. altum are not branched, and secondly, 

 that branched cells are occasionally met with in other species 

 of Cylindrcecium. The " branched " condition of zooecia 

 might be accounted for in three ways : — 



1. The main zooecium may bifurcate or may produce a 

 secondary zooecium by budding, the polypide of the bud later 

 remaining in organic connexion with that of the primary cell. 

 Angwinella palmaia, Van Beneden, presents the nearest 

 resemblance to a Cylindrcecium with branching zooecia. 



2. Embryos may settle down on the zooecial tubes and 

 there develop ; such a condition is well seen in the Hydroid 

 Tuhularia indivisa. 



3. Portions of stolon may become fixed to the walls of a 

 zooecium, and a zooecium develop at that point. 



Judging from the specimen, any one or all of these events 

 may have taken place, for zooecia can be seen growing from the 

 walls of primary zooecia and unconnected with stolon ; others 

 again have a portion of stolon-tube growing from the attached 

 base ; and, lastly, one cell has bifurcated. 



Cylindroecium papuense. Busk. 

 Hah. Growing on Amathiw. 



