CLAVATELLA PROLIFERA. 213 



verticil of from six to eight capitate tentacles round the base of a short conical hypostome. It is 

 very contractile, and in extreme contraction assumes a short, thick, flask-shaped form. During 

 contraction the body is seen to be marked by fine, regular, closely set transverse rugae. 



A longitudinally fibrillated layer can be distinctly demonstrated beneath the ectoderm on 

 the body of the hydranth, through the entire length of which it may be traced (fig. 11). The 

 endoderm presents a peripheral layer of large cells with clear colourless contents, and an axial 

 layer which lines the somatic cavity and is composed of much smaller cells containing coloured 

 granules. In the ectoderm no distinct cellular structure can be demonstrated, but it contains 

 numerous thread-cells imbedded in it. 



The tentacles (fig. 3) present the usual septate condition. The spaces included between the 

 septa have their axes occupied by an accumulation of granular protoplasm, often looking like a 

 continuous axile column running through the whole length of the tentacle. The capitulum in 

 which the tentacle terminates is very well marked, and is loaded with large thread-cells. 



The Gonophores. — The gonophores (fig. 1 and figs. 4 — 10) are borne on one or two short- 

 branched tubular peduncles, which spring from the hydranth at the spot where the basal dilatation 

 is seen in the extended hydranth to pass into the narrower, more distal portion of the body. When 

 two of the branched peduncles are present they are situated upon opposite points of the body. 

 There are generally two or three gonophores, in various stages of development, in a cluster, each 

 being borne on the extremity of one of the branches of the peduncle, whose tube com- 

 municates freely on one side with the digestive cavity of the gonophore, and on the other with that 

 of the hydranth. 



The fully formed gonophore (fig. 4) is medusiform, but yet singularly exceptional among 

 medusae, for its umbrella is never developed into a swimming-bell, and locomotion is performed by 

 peculiarh' constructed marginal tentacles, on which this strange ambulatory planoblast is capable 

 of creeping about from place to place. 



The gonophore is dome-shaped, and when viewed from its dorsal aspect under the carefully 

 regulated action of the compressorium, it will be seen to be occupied by a large central cavity, 

 from the circumference of which six short but wide tubes radiate at equal intervals towards the 

 margin of the dome, where they meet a wide circular canal, which runs parallel to this margin 

 and close to it (figs. 4, 5). 



At points corresponding to those at which the radiating canals meet the circular the margin 

 is extended into six long tentacles, each of which divides into two branches at some distance 

 beyond its middle. The two branches are situated in a radial plane, so that one is internal or 

 looks towards the axis of the medusa, the other external or directed away from the axis. The 

 external branch terminates in a capitulum of thread-cells, the internal one in a slightly swollen 

 extremity, which carries a minute suctorial disc (fig. 7). The endoderm of the tentacle and of its 

 branches is large-celled, giving to them a somewhat septate appearance; but the axis is pervious, 

 being traversed by a tubular prolongation of the circular marginal canal. 



In the centre of the under surface of the dome-shaped disc is the quadrangidar aperture of 

 the mouth, sometimes scarcely raised above the general surface, and sometimes elevated on a 

 prominent conical projection. It is entirely destitute of lobes and of tentacular appendages. 



On the outer side of the base of every tentacle is a very distinct ocellus, consisting of a heap 

 of red pigment-granules, in which a clear refracting spherule may sometimes be seen to be 

 immersed, and over which a transparent, slightly elevated extension of the ectoderm may be 



