1865.] Hincks on Zoophytes : the History of (heir Development. 417 



the two classes. The boundary, on one side of which is found the 

 Gono-zooid of Tubularia indivisa, with its fully-developed swimming- 

 bell, exhibiting canals, an orifice, and even slight contractility, and on 

 the other, the Gono-zooid of Coryne gravata (Wright), or Syncoryna ra- 

 mosa (Loven), with rudimentary mouth and tentacles, and which never 

 becomes detached, can only be regarded as purely artificial. We believe 

 that it is wiser in all respects to maintain unimpaired the continuity 

 of the series, and not to break, for purposes of convenience or other- 

 wise, the chain of links which connects the lowest form with the 

 highest.* 



Again, Professor Allman long ago enunciated the doctrine that the 

 fixed sexual buds of the Hydroida possess in all cases " a true Me- 

 dusal structure in a more or less degraded or disguised condition ; " 

 and in his recent report he lays it down that " the closed generative 

 sac of a Clava (vide Plate i. fig. la), or a Hydractinia (Plate i. 

 fig. 5), is an easily understood modification of a Medusa." But why 

 this way of putting it ? " Medusal structure " is modified polypite 

 structure. The fundamental element, as it were, of the Hydroid life- 

 series is the polypite, as the leaf of the life-series of the plant. It is 

 this element which is " disguised " in some portions of the reproduc- 

 tive scale, and which it is at times somewhat difficult to recognize 

 beneath its adaptive dress. We should reverse Professor Allman's 

 proposition, and say that the (so-called) Medusa is a modification of 

 the " closed generative sac of the Clava," or rather of the polypite, of 

 which the latter is itself an adaptation. And instead of tracking " Me- 

 dusal structure " amongst the disguises of the reproductive system, we 

 should rather start from the simple element which constitutes the com- 

 mon base of the Hydroid organism, and trace the gradual evolution 

 from it of the more complex forms which culminate in the free sexual 

 zooid. With this view we most truly interpret the facts which are 

 actually before us ; for the polypite element is recognizable from one 

 end of the series to the other, but the reproductive sacs of Clava and 

 other Hydroids are without a trace of Medusan structure, and to say 

 that this structure exists in them in "a degraded or disguised con- 

 dition," really means no more than to say that the statue exists in a 

 degraded or disguised condition in the block of marble. Professor 

 Allman would recognize the " Medusal " element throughout the 

 reproductive series ; we, on the contrary, would rather recognize the 

 polypite everywhere, and dropping altogether a term which seems at 

 least to imply an essentially distinct mode of structure, we should say 

 that the Gono-zooid of the Hydroid Zoophyte is a Hydra more or less 

 modified for the discharge of the sexual functions — attaining in its 

 highest form a free existence, and becoming locomotive by the con- 

 version of its tentacles into a natatory organ. 



The whole subject under many of its aspects is one which must 

 have an interest for the general reader, though he may not be willing 

 to undertake the study of a new language for the sake of it. It has 

 been our simple object to translate the later views of the development 



* Professor Huxley has taken the same view in his great work on the ' Oceanic 

 Hydrozoa,' p. 137. 



VOL. II. 2 G 



