Mr. R. Q. Couch on the Morphology of Zoophytes. 163 



and at others assuming the appearance of having an enlarged 

 head and a narrow and contracted tail. But having once fixed 

 itself, it remains rooted ever after. From the period it first be- 

 comes fixed it speedily undergoes a change in tint, but this how- 

 ever would hardly be perceptible except to a practised eye. 

 When this has taken place small fibres are given out from the 

 base, or all that portion in contact with the glass. These consti- 

 tute the roots by which the creature becomes fixed. From this 

 point it quickly rises into the arborescent form of the adult. This 

 is a remarkable change ; for here we see a creature in its youngest 

 form moving about with almost the irregularity of voluntary mo- 

 tion, yet in a short time becoming rooted and taking on so much 

 of the vegetable form and appearance, as to have required, at the 

 hand of Ellis, repeated observations and accurate demonstrations 

 to persuade us to the contrary. The seed being fixed, the upper 

 portion becomes elongated without any distinction of parts, and 

 the first joint of the creature is formed. Taking the sea- thread, 

 Laomedea geniculata, as an example best calculated to show the 

 analogies between the formation of the polype cells and ovarian 

 vesicles, the central pulp of the seed becomes the central gra- 

 nular pulp of the adult. After the ovule has become superiorly 

 elongated to a distance equal to the usual length of the cell and 

 its footstalk, it enlarges and becomes bulbous. All is now one 

 undefined mass ; but in the course of a few hours the stalk be- 

 comes shrivelled, and the bulbous termination acquires a deeper 

 tint towards the centre and lighter towards the circumference. 

 At first this central shade is slight and indistinct, but it soon be- 

 comes darker and more defined. As this condensation or orga- 

 nization advances, the pulp becomes more transparent at its cir- 

 cumference, and darker towards the centre. At this stage the 

 transparent circumference appears to be drawn into transverse 

 folds, as if from a force acting towards the centre, and leaves be- 

 hind a transparent horny covering which eventually forms the 

 walls of the future cell. In this way the whole of the pulp be- 

 comes separated from the investing sheath. This being eff'ected, 

 the upper edge of the bulbous portion of the pulp acquires a ser- 

 rated edge, which in a short time becomes more and more di- 

 stinct and enlarged, and finally is produced into finger-like pro- 

 longations forming the tentacula of the polype. It is by an ex- 

 tension of development that the horny cell is opened, and not by 

 any mechanical pressure as has been supposed, since the only 

 source of pressure is from the polype, and that is not in contact 

 with it at the time. In this the polypes are formed from the 

 central granular pulp in all the Sertularian species, having but 

 very slight modifications in the difi'erent genera. The prolon- 

 gation of the stem is formed in precisely the same manner, but 



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