GEMMARIA IMPLEXA. 235 



circular canal (fig 3). During contraction four meridional farrows may be seen on the outer 

 siu-flice of the umbrella, alternating with the radiating canals, and extending from the summit to 

 the codononostonic. 



The mannbrium extends through aljout one half the vertical diameter of the mubrella. It 

 is nearly cylindrical, destitute of oral tentacles or lobes, and having the month snrroundcd l)y a 

 circle of minute thread-cells. 



A still more remarkable feature than tliat derived from the prescnci; of the thrcad-ccll- 

 l)earing sacs in the umbrella is atlbrdcd by the two marginal tentacles (tig. 3, 4). Along its entire 

 length from the bulbous expansion at its base to its tip each tentacle carries oval capsules filled 

 with thread-cells. They are thickly set along the whole length of the tentacle, each arising by a 

 ])edunclc from its outer side. The capsule itself carries a pencil of long vibratile cilia on its 

 summit. Along the sides of its peduncle small spherical masses containing granules are 

 irregularly scattered. These appendages of the marginal tentacles would seem to have their 

 representatives in what appear to be very similar bodies figured by Gegenbaur in Zanclea. 



Whether, however, the pedunculated capsules which are carried on the marginal tentacles 

 of Gcmmaria resendjle in all respects the tentacular appendages of Zanclea is a question which 

 remains open for future observation, but it is certain that these bodies in Gemmaria present a 

 phenomenon to which nothing similar has yet been recorded in any other hydroid. 



Some years ago I dredged oft' the Forfarshire coast a colony of Gemmaria implexa, which, 

 after remaining for about a fortnight in a jar of sea-w^ater, threw off' its medusje. On examining 

 these with a hand-lens as they floated through the water I was struck by the appearance of a 

 mould-like growth with which many of them seemed covered, and for a moment I thought that 

 they had become infested by some low parasitic vegetation. That this, however, was something 

 very different from what it appeared to be soon became evident, for wdien the little medusa was 

 touched ever so slightly with the point of a needle the whole of the flocculent mass instantly 

 vanished. 



It needed, however, a higher power of the microscope to reveal the true nature of this 

 phenomenon and show that the apparently parasitical growth consisted of the enormously 

 elongated peduncles of the thread-cell-bearing capsules, each of which, as it now proved, 

 had the po\ver wdiile still carrying the capsule on its extremity of extending itself to a 

 length wdiich considerably surpassed that of the longer or vertical diameter of the umbrella 

 (see fig. 3). 



AVhile the medusa continued to float undisturbed through the water the peduncle would 

 remain projected in a straight line from the tentacle, becoming at the same time amazingly 

 attenuated, but on the least disturbance it would suddenly shorten itself to less than one 

 twentieth part of its length when extended, drawing the capsule back with it in its contraction. 

 Tlie extended condition of the peduncles was seen only while the medusa was passively floating 

 in the water, while engaged in active locomotion the peduncles were always contracted. 



The small spherical masses Avhich are attached to the sides of the peduncle become widely 

 separated from one another on extension, and the whole peduncle with its terminal capsule was 

 seen during the extended condition to be in a state of constant vibration. This was due to the 

 pencil of long fine vibratile cilia which the capsule carried on its summit. 



I believe that the remarkable phenomenon now' described presents us with a case of true 

 .sarcode extension and contraction, and that the peduncles of the thread-cell-bearing capsides 



