180 RKPllESENTATIOX OF THE 



dages — which we may term either organs or zooids — are 

 adapted to fulfil diflereiit functions for the benefit of the 

 wdiole — the outer polypes being metamorphosed into tenta- 

 cular organs of offence and defence, the inner into stomachs, 

 and certain others into spermatic or ovarian cysts.* The 

 same remark will apply to many of the compound Physo- 

 phorida and Calycophorida. 



With such cases before us, it seems very clear that the 

 detachment of reproductive zooids, as in one form of alter- 

 nation of generations, is a point even of less importance 

 than their elaborate oro-anization, in marlvino; them out as 

 of a different nature from the reproductive organs of the 

 higher animals ; for when we come to species in which the 

 organs of alimentation, prehension, &c., acquire a sort of 

 independent vitality, it is only to be expected that those of 

 reproduction should also appear as free zooids. *|" 



§ 9. If from the Animal we turn to the Vegetable 

 Kingdom, we shall find that there likewise a correspondence 

 may be traced between certain processes in the fructifica- 

 tion of the Phanerogamia and the alternation of the ferns 

 and allied Cryptogamia. 



* Dr. T. S. Wriglit, Ed. N. Phil. Jour., April, 1857, p. 305. See also 

 a former note in Chapter V., 2. 



f The view here contended for — viz., that the gamomorphic zooids are 

 merely reproductive organs, isolated and hyper-organized into the simiH- 

 tude of distinct animals, may appear to be opposed by certain facts in the 

 alternation of Syllis and aUied Annelida. Dr. A. Thomson quotes obser- 

 vations of Leuckart and Schultze to the effect that the parent annelidan 

 arrives itself eventually at sexual perfection, after having given off a num- 

 ber of sexual zooids by the caudal gemmation. (Note to Article on the 

 " Ovum" in the Cyclopaedia of Anatomy and Physiology, p. 33). As the 

 animal, therefore, comes ultimately to possess reproductive organs wdthin 

 ts own body, we have not, it may be said, to seek for them in the free 

 Zooids. Not knowing the exact details, I can only suggest thatif the for- 

 mation of these organs is preceded by a process of gemmation from a 

 local centre, as in the case of the detached zooids, then the region of the 

 body in which they occur ma}^ fairly rank as one of the series, which re- 

 mains attached simply because it is the last formed. 



